sense quantum channel
阅读说明:本技术 广义量子通道 (sense quantum channel ) 是由 蒋良 沈超 诺耿朱 维克托·V·艾伯特 斯特凡·克拉斯塔诺夫 米歇尔·德沃尔特 罗伯特· 于 2017-11-10 设计创作,主要内容包括:根据一些方面,提供了一种量子信息系统,该量子信息系统包括:辅助量子比特;量子数位,其耦合到该辅助量子比特;检测器,其被配置成基于辅助量子比特的量子态来生成检测结果;以及驱动源,其耦合到量子数位和辅助量子比特,并且被配置成基于该检测结果将至少一个量子数位驱动信号施加至量子数位以及基于该检测结果将至少一个量子比特驱动信号施加至量子数位。(According to aspects, there is provided a quantum information system that includes an ancillary qubit, a qubit coupled to the ancillary qubit, a detector configured to generate detection results based on quantum states of the ancillary qubit, and a drive source coupled to the qubit and the ancillary qubit and configured to apply at least qubit drive signals to the qubit based on the detection results and at least qubit drive signals to the qubit based on the detection results.)
1, a quantum information system, comprising:
an auxiliary qubit;
a qubit coupled to the ancillary qubit;
a detector configured to generate a detection result based on a quantum state of the ancillary qubit; and
a drive source coupled to the qubit and the auxiliary qubit and configured to apply at least qubit drive signals to the qubit based on the detection results and at least qubit drive signals to the qubit based on the detection results.
2. The quantum information system of claim 1, further comprising a controller coupled to the drive source and the detector, wherein the controller is configured to:
receiving a detection signal indicative of the detection result from the detector;
controlling the drive source to drive the qubit using the at least qubit drive signals, and
controlling the drive source to drive the qubit using the at least qubit drive signals.
3. The quantum information system of claim 2, wherein the controller is further configured to:
obtaining an indication of a desired quantum channel;
determining the at least qubit drive signals based on the indication of the desired quantum channel, and
determining the at least qubit drive signals based on the indication of the desired quantum channel.
4. The quantum information system of claim 3, wherein the indication of the desired quantum channel is received from a user.
5. The quantum information system of claim 3, wherein the indication of the desired quantum channel comprises a plurality of Kraus operators.
6. The quantum information system of claim 5, wherein the plurality of Kraus operators constitutes a minimum Kraus representation of the desired quantum channel.
7. The quantum information system of claim 6, wherein obtaining the indication of the desired quantum channel comprises determining the plurality of Kraus operators that constitute the smallest Kraus representation of the desired channel from or more other operators.
8. The quantum information system of claim 7, wherein the controller is further configured to determine a plurality of joint unitary operators, each of the plurality of joint unitary operators configured to operate on a joint system comprising the ancillary qubits and the qubits.
9. The quantum information system of claim 8, wherein the controller is further configured to create a binary tree structure associated with the plurality of unitary operators.
10. The quantum information system of claim 9, wherein the controller is further configured to determine each of the plurality of joint unitary operators based on diagonalization of a sum of a subset of the plurality of Kraus operators rooted at an associated node of the binary tree structure.
11. The quantum information system of claim 10, wherein the controller is further configured to determine a qubit unitary operator, a qubit unitary operator, and a second qubit unitary operator associated with each of the plurality of joint unitary operators and based on each of the plurality of joint unitary operators.
12. The quantum information system of claim 11, wherein the controller is further configured to:
determining the at least qubit drive signals based on the qubit unitary operator and the second qubit unitary operator, and
determining the at least qubit drive signals based on the qubit unitary operator.
13. The quantum information system of claim 3, wherein the desired quantum channel comprises an initialization channel for the qubit.
14. The quantum information system of claim 3, wherein the desired quantum channel comprises a stabilization channel for the quantum digit.
15. The quantum information system of claim 3, wherein the desired quantum channel comprises a quantum error correction channel for the quantum digital bit.
16. A quantum information system according to claim 3, wherein the desired quantum channel comprises a positive operator value measurement of the qubit.
17. The quantum information system of claim 3, wherein the desired quantum channel comprises a quantum instrument channel.
18. The quantum information system of claim 1, wherein the ancillary qubit is a superconducting qubit.
19. The quantum information system of claim 18, wherein the auxiliary qubit is included at least on a josephson junction.
20. The quantum information system of claim 19, wherein the ancillary qubit comprises a transmon qubit.
21. The quantum information system of claim 1, wherein the quantum digital bit comprises a quantum oscillator.
22. The quantum information system of claim 21, wherein the quantum oscillator comprises electromagnetic radiation in a cavity.
23. The quantum information system of claim 22, wherein the cavity is a stripline cavity.
24. The quantum information system of claim 22, wherein the cavity comprises a three-dimensional metal cavity.
25. A quantum information system according to claim 1, wherein the drive source comprises a source of electromagnetic radiation.
26. A quantum information system according to claim 25, wherein said electromagnetic radiation source comprises a microwave pulse generator.
27. The quantum information system of claim 1, wherein the detector comprises a readout cavity.
28, a method of operating a quantum information system, the quantum information system including a qubit coupled to an ancillary qubit, thereby forming a qubit-qubit system, the method comprising:
applying th unitary operation to the qubit system;
generating a detection result based on the quantum state of the ancillary qubit; and
applying a second unitary operation to the qubit system based on the detection result.
29. The method of claim 28 further comprising initializing said ancillary qubits prior to applying said unitary operation.
30. The method of claim 28, further comprising:
obtaining an indication of a desired quantum channel;
determining at least qubit drive signals based on the indication of the desired quantum channel, and
determining at least qubit drive signals based on the indication of the desired quantum channel.
31. The method of claim 30, wherein the indication of the desired quantum channel is received from a user.
32. The method of claim 30, wherein the indication of the desired quantum channel comprises a plurality of Kraus operators.
33. The method of claim 32, wherein the plurality of Kraus operators constitutes a minimum Kraus representation of the desired quantum channel.
34. The method of claim 33, wherein obtaining the indication of the desired quantum channel comprises determining the plurality of Kraus operators that constitute the minimum Kraus representation of the desired channel from or more other operators.
35. The method of claim 34 further comprising determining a plurality of joint unitary operators, each of the plurality of joint unitary operators configured to operate on a joint system comprising the ancillary qubits and the qubits.
36. The method of claim 35, further comprising: a binary tree structure associated with the plurality of unitary operators is determined.
37. The method of claim 36, further comprising determining each of the plurality of joint unitary operators based on diagonalization of a sum of a subset of the plurality of Kraus operators rooted at an associated node of the binary tree structure.
38. The method of claim 37 further comprising determining a qubit unitary operator, a qubit unitary operator, and a second qubit unitary operator associated with each of the plurality of joint unitary operators and based on each of the plurality of joint unitary operators.
39. The method of claim 38, further comprising:
determining the at least qubit drive signals based on the qubit unitary operator and the second qubit unitary operator, and
determining the at least qubit drive signals based on the qubit unitary operator.
40. The method of claim 30, wherein the desired quantum channel comprises an initialization channel for the qubit.
41. The method of claim 30, wherein the desired quantum channel comprises a stabilization channel for the quantum digit.
42. The method of claim 3, wherein the desired quantum channel comprises a quantum error correction channel for the quantum digital bit.
43. The method of claim 30, wherein the desired quantum channel comprises a positive operator value measurement of the qubit.
44. The method of claim 30, wherein the desired quantum channel comprises a quantum instrument channel.
45. The method of claim 28, wherein the ancillary qubit is a superconducting qubit.
46. The method of claim 45, wherein the auxiliary qubit is included at least on a Josephson junction.
47. The method of claim 46, wherein the ancillary qubit comprises a transmon qubit.
48. The method of claim 28, wherein the quantum digital bit comprises a quantum oscillator.
49. The method of claim 48, wherein the quantum oscillator comprises electromagnetic radiation in a cavity.
50. The method of claim 49, wherein the cavity is a stripline cavity.
51. The method of claim 49, wherein the cavity comprises a three-dimensional metal cavity.
52. The method of claim 28, wherein the drive signal comprises an electromagnetic radiation signal.
53. The method of claim 52, wherein the electromagnetic radiation signal comprises a microwave radiation signal.
54. The method of claim 28, wherein the detector comprises a readout cavity.
55. At least non-transitory storage media encoded with executable instructions that, when executed by at least processors, cause the at least processors to perform a method of creating a -sense quantum channel, wherein the method comprises:
obtaining a plurality of Kraus operators associated with a desired quantum channel;
generating a plurality of unitary joint operations associated with a joint qubit system based on the Kraus operator;
determining th unitary joint operation of a plurality of unitary joint operations to be performed on the joint qubit system, and
determining two unitary qubit-only operations and unitary qubit-only operations based on the th unitary joint operation.
56. The at least non-transitory storage media of claim 55, wherein obtaining the plurality of Kraus operators comprises:
receiving an indication of a desired quantum channel; and
determining a minimum Kraus representation of the quantum channel based on the indication.
57. The at least non-transitory storage media of claim 56, wherein the indication of the desired channel includes a plurality of non-minimum Kraus operators.
58. The at least non-transitory storage media of claim 56, wherein the indication of the desired channel comprises a super operator matrix, a Choi matrix, or a Jamiolkowski matrix.
59. The at least non-transitory storage media of claim 55, wherein the method further comprises generating a binary tree structure associated with the plurality of unitary joint operations.
60. The at least non-transitory storage media of claim 59, wherein each node of the binary tree structure is associated with a respective unitary joint operation of the plurality of unitary joint operations.
61. The at least non-transitory storage media of claim 60, wherein each leaf of the binary tree structure is associated with a Kraus operator of the desired quantum channel.
62. The at least non-transitory storage media of claim 55, wherein the unitary qubit-only operation is a selective number-dependent arbitrary phase operation.
Technical Field
The technology described herein relates generally to quantum information systems. In particular, the present application relates to systems and methods for controlling quantum mechanical systems.
Background
As in in conventional information processing where information is stored in or more bits, quantum information may be stored in or more qubits called "qubits". The qubits may be physically implemented in any two-state Josephson mechanical system such as photon polarization, electron spin, nuclear spin, or various characteristics of superconducting Severson junctions (Josephson junctions), such as charge, energy, or current direction.
In addition, "quantum digital" (qudit), a quantum system having a number "d" of discrete quantum states, may be used to store and process quantum information. A qubit is a specific example of a qubit with d-2. A quantum digital bit may be implemented using a physical quantum system having multiple states with multiple energy levels, such as a quantum oscillator.
Disclosure of Invention
The present application relates generally to systems and methods for controlling quantum mechanical systems.
According to aspects, there is provided a qubit information system including an ancillary qubit, a qubit coupled to the ancillary qubit, a detector configured to generate detection results based on quantum states of the ancillary qubit, and a drive source coupled to the qubit and the ancillary qubit and configured to apply at least qubit drive signals to the qubit based on the detection results and at least qubit drive signals to the qubit based on the detection results.
According to embodiments, the quantum information system further includes a controller coupled to the drive source and the detector, wherein the controller is configured to receive a detection signal from the detector indicative of a detection result, control the drive source to drive the qubit using at least qubit drive signals, and control the drive source to drive the qubit using at least qubit drive signals.
According to embodiments, the controller is further configured to obtain an indication of a desired quantum channel, determine at least qubit drive signals based on the indication of the desired quantum channel, and determine at least qubit drive signals based on the indication of the desired quantum channel.
According to , an indication of a desired quantum channel is received from a user.
According to embodiments, the indication of the desired quantum channel includes a plurality of Kraus operators.
According to embodiments, the multiple Kraus operators constitute a minimum Kraus representation of the desired quantum channel.
According to embodiments, obtaining the indication of the desired quantum channel includes determining, from or more other operators, a plurality of Kraus operators that constitute a minimum Kraus representation of the desired channel.
According to embodiments, the controller is further configured to determine a plurality of joint unitary operators, each of the plurality of joint unitary operators configured to operate on a joint system comprising an ancillary qubit and a qubit.
According to embodiments, the controller is further configured to create a binary tree structure associated with the plurality of unitary operators.
According to embodiments, the controller is further configured to determine each of the plurality of joint unitary operators based on diagonalization of a sum of a subset of the plurality of Kraus operators rooted at an associated node of the binary tree structure.
According to embodiments, the controller is further configured to determine a qubit unitary operator, a qubit unitary operator, and a second qubit unitary operator associated with each of the plurality of joint unitary operators and based on each of the plurality of joint unitary operators.
According to embodiments, the controller is further configured to determine at least qubit drive signals based on a qubit unitary operator and a second qubit unitary operator and to determine at least qubit drive signals based on the qubit unitary operator.
According to embodiments, it is desirable that the quantum channel include an initialization channel for the qubit.
According to embodiments, it is desirable that the quantum channel include a stabilization channel for the quantum digit.
According to embodiments, it is desirable that the quantum channel include a quantum error correction channel for the quantum digit.
According to , wherein the desired quantum channel comprises a positive operator value measurement of a quantum digit.
According to embodiments, it is desirable that the quantum channel comprise a quantum instrument channel.
According to , the ancillary qubits are superconducting qubits.
According to , the auxiliary qubits are included at least on a josephson junction.
According to , the ancillary qubits include a transmon qubit.
According to , the quantum digital bit includes a quantum oscillator.
According to embodiments, a quantum oscillator includes electromagnetic radiation in a cavity.
According to the cavity is a stripline cavity.
According to embodiments, the cavity comprises a three-dimensional metal cavity.
According to , the drive source includes a source of electromagnetic radiation.
According to , the electromagnetic radiation source includes a microwave pulse generator.
According to embodiments, the detector includes a readout cavity.
aspects relate to methods of operating a quantum information system that includes a qubit coupled to a qubit to form a qubit-qubit system that includes applying a th unitary operation to the qubit-qubit system, generating a detection result based on a quantum state of the qubit, and applying a second unitary operation to the qubit-qubit system based on the detection result.
According to embodiments, the method further includes initializing the ancillary qubits prior to applying the unitary operation.
According to embodiments, the method further includes obtaining an indication of a desired quantum channel, determining at least qubit drive signals based on the indication of the desired quantum channel, and determining at least qubit drive signals based on the indication of the desired quantum channel.
According to , an indication of a desired quantum channel is received from a user.
According to embodiments, the indication of the desired quantum channel includes a plurality of Kraus operators.
According to embodiments, the multiple Kraus operators constitute a minimum Kraus representation of the desired quantum channel.
According to embodiments, obtaining the indication of the desired quantum channel includes determining, from or more other operators, a plurality of Kraus operators that constitute a minimum Kraus representation of the desired channel.
According to embodiments, the method further includes determining a plurality of joint unitary operators, each of the plurality of joint unitary operators configured to operate on a joint system including an ancillary qubit and a qubit.
According to embodiments, the method further includes determining a binary tree structure associated with the plurality of unitary operators.
According to embodiments, the method further includes determining each of the plurality of joint unitary operators based on diagonalization of a sum of a subset of the plurality of Kraus operators rooted at an associated node of the binary tree structure.
According to embodiments, the method further includes determining a qubit unitary operator associated with each of the plurality of unitary joint operators and based on each of the plurality of unitary joint operators, a qubit unitary operator, and a second qubit unitary operator according to embodiments, the method further includes determining at least qubit drive signals based on the qubit unitary operator and the second qubit unitary operator, and determining at least qubit drive signals based on the qubit unitary operator.
According to embodiments, it is desirable that the quantum channel include an initialization channel for the qubit.
According to embodiments, it is desirable that the quantum channel include a stabilization channel for the quantum digit.
According to embodiments, it is desirable that the quantum channel include a quantum error correction channel for the quantum digit.
According to , the quantum channel is expected to include a positive operator value measurement of a quantum digit.
According to embodiments, it is desirable that the quantum channel comprise a quantum instrument channel.
According to , the ancillary qubits are superconducting qubits.
According to , the auxiliary qubits are included at least on a josephson junction.
According to , the ancillary qubits include a transmon qubit.
According to , the quantum digital bit includes a quantum oscillator.
According to embodiments, a quantum oscillator includes electromagnetic radiation in a cavity.
According to the cavity is a stripline cavity.
According to embodiments, the cavity comprises a three-dimensional metal cavity.
According to , the drive signal includes an electromagnetic radiation signal.
According to , the electromagnetic radiation signal includes a microwave radiation signal.
According to embodiments, the detector includes a readout cavity.
aspects relate to at least non-transitory storage media encoded with executable instructions that, when executed by at least processors, cause the at least processors to perform a method of creating a sense quantum channel, wherein the method includes obtaining a plurality of Kraus operators associated with a desired quantum channel, generating a plurality of unitary joint operations associated with a joint qubit-qubit system based on the Kraus operators, determining a th unitary joint operation of the plurality of unitary joint operations to be performed on the joint qubit-qubit system, and determining two unitary qubit-only operations and unitary qubit-only operations based on a th unitary joint operation.
According to embodiments, obtaining a plurality of Kraus operators includes receiving an indication of a desired quantum channel and determining a minimum Kraus representation of the quantum channel based on the indication.
According to embodiments, the indication of the desired channel includes a plurality of non-minimum Kraus operators.
According to embodiments, the indication of the desired channel includes a super operator matrix, a Choi matrix, or a Jamiolkowski matrix.
According to embodiments, the method further includes generating a binary tree structure associated with the plurality of unitary joint operations.
According to embodiments, each node of the binary tree structure is associated with a respective unitary joint operation of a plurality of unitary joint operations.
According to embodiments, each leaf of the binary tree structure is associated with a Kraus operator of the desired quantum channel.
According to embodiments, the unitary qubit-only operation is a selective number-dependent arbitrary phase operation.
The foregoing is a non-limiting summary of the invention, which is defined by the appended claims.
Drawings
Various aspects and embodiments are described with reference to the following drawings, which are not to scale.
Fig. 1 is a block diagram of a quantum information system according to embodiments.
Fig. 2 depicts a quantum circuit for constructing an arbitrary quantum channel according to embodiments.
Fig. 3 depicts a binary tree structure for constructing arbitrary quantum channels according to embodiments.
Fig. 4 is a flow diagram of a method of operating a quantum information system according to embodiments.
Fig. 5 is a block diagram of a quantum information system based on cavity quantum electrodynamics, according to embodiments.
Fig. 6 depicts an exemplary spectrum of a transmon qubit of a quantum oscillator coupled to a storage cavity in accordance with embodiments .
Fig. 7 depicts an energy level diagram of a transmon qubit of a quantum oscillator coupled to a storage cavity in accordance with embodiments.
FIG. 8 is a block diagram of a computer system according to embodiments.
Fig. 9 is a flow diagram of a method of operating a quantum information system according to embodiments.
Fig. 10 is a block diagram of different types of quantum channels classified according to their outputs.
Detailed Description
Conventional quantum information processing schemes encode information in or more two-level quantum systems (i.e., "qubits"), the state of a single qubit may be represented by a quantum state | ψ >, which may be an arbitrary superposition of two quantum states |0> and |1>, e.g., | ψ > - α |0> + β |1>, where α and β are complex numbers representing the probability magnitudes of the logical qubits in states |0> and |1>, respectively.
To perform useful quantum information processing, conventional quantum information systems initialize sets of qubits to specific quantum states, implement sets of
Conventional quantum information systems typically perform detection of qubits by measuring which quantum state of sets of possible quantum states each qubit is in.this type of measurement is referred to as a projection measurement (sometimes referred to as a projection). an example of a projection measurement includes measuring the quantum state of a qubit on a particular basis to determine a detection result of |0> or |1 >.
The inventors have recognized and appreciated that unique and powerful quantum information processing may be achieved using a more general type of quantum operation known as sense quantum channel and also known as fully positive apodization (CPTP) mapping, which includes not only the unitary quantum and projection measurements described above, but also non-unitary quantum state evolution and sense quantum measurements known as positive operator valued measures (pomms)>Conversion from density matrix
Mixed states of representation, wherein i marks each pure quantum state forming the mixed state, and the coefficient piNon-negative and sum to 1.However, the inventors have recognized and appreciated that any arbitrary CPTP mapping may be implemented for a qubit and an additional single ancillary qubit only, as well as circuit depths that vary logarithmically with the dimension of the qubit.
Referring to fig. 1, a quantum information system 101 for constructing a quantum channel according to embodiments includes a
Examples of superconducting qubits include superconducting charge qubits where the two quantum states relate to the charge of the superconductor, superconducting flux qubits where the two quantum states are the direction of current flow, and superconducting phase qubits where the two quantum states are two energy eigenstates.
A drive source 150 is coupled to
The
As will be described in more detail below, the
The above process is discussed in theoretical detail below, followed by an example implementation based on a particular implementation using a cQED device.
Obtaining a minimum Kraus representation of a quantum channel
Quantum channels (i.e., CPTP) can be represented using the Kraus representation:
in the
To efficiently construct CPTP mappings according to embodiments, it is convenient to perform the Kraus representation with the minimum number of Kraus operators, referred to as the Kraus rank of the CPTP mapping2A linear independent operator, so that the Kraus rank is not greater than d2. Efficient computational techniques known in the art can be used to convert the non-minimal representation of the CPTP map to a minimal Kraus representation. For example, the Kraus representation may be converted to a Choi matrix (d)2×d2Hermitian matrix) and derived therefrom the minimum Kraus representation as described in m.d. choi, Linear Algebra appl, 10,285(1975), the entire content of which and at least for its discussion of techniques for determining the minimum Kraus representation is incorporated herein by reference. (in the event that any term used herein conflicts with the use of that term in Choi, the term should be given the most consistent meaning to those of ordinary skill in how to understand its use herein.) the second approach is to compute an overlap matrix
And then to make it diagonalized,if the original representation is redundant, the new Kraus accounts forIs the most economical representation, where of them are zero matrices.In some implementations , the quantum channel may be provided in a representation other than the Kraus representation (e.g., a super operator matrix representation, a Jamiolkowski/Choi matrix representation). these alternative representations may also be converted to a minimum Kraus representation.
Since the CPTP mapping is linear in the density matrix ρ, ρ can be considered as a vector and the super-operator acting on the quantum states represented by the density matrix
The matrix form of (a) can be written as:
or
Wherein the content of the first and second substances,
is the state of the quantum system after application of the quantum channel.The matrix form of the quantum channel also allows the quantum channel to be characterized using the determinant of the matrix.
Obtaining a super operator matrix representation of a quantum channel from a Kraus representation is relatively simple compared to obtaining the Kraus representation from a super operator matrix representation. Given the channel in Kraus, the super operator matrix T can be obtained as follows:
wherein, KiIs the Kraus operator (where there are N different Kraus operators), and Ki *Is the Kraus operator KiComplex conjugation of (a). However, obtaining the Kraus representation from the super operator matrix T uses channel state duality (i.e., Jamiolkowski-Choi isomorphism), known from it for having a d-dimensional Hilbert space
Each channel of the system ofAs follows and with respect to having a hilbert spaceThe states (density matrix) () of the two subsystems correspond to:
wherein the content of the first and second substances,
is the maximum entangled state of the two subsystems and τ is the Jamiolkowski matrix representation of the quantum channel. ChoThe i-matrix M is simply the Jamiolkowski matrix τ multiplied by the dimension of the hilbert space, i.e., a constant multiple of the constant d. The relationship between Choi matrix M and super operator matrix T is as follows:Tij,mn=Mim,jnballoon catheter (formula 5)
As a density matrix, τ is Hermite. Furthermore, if and only if
Fully positive, τ is semi-positive; if it is notIs apodized, then we rank τ the Choi matrix M can be converted to a Kraus representation using the following fact if M is diagonalized:
wherein vi is d of τ2A dimensional feature vector. Then, by mixing
The d × d matrix is rearranged to obtain the Kraus operator. Non-zero eigenvalue λi, numerical calculations are performed, wherein the data may be obtained by, for example, having a value of less than 10-10All eigenvalues of the value of (c) are set to theGeneral structural theory of quantum channels
Having described the above techniques for obtaining a minimum Kraus representation of a particular quantum channel, in accordance with embodiments, techniques for physically constructing a desired quantum channel are described embodiments, any arbitrary CPTP mapping is constructed using a binary tree scheme
Are associated. For sheetsA plurality of auxiliary qubits to be applied to the qubit,is the lowest, which is the meaning herein when the structure of the equivalent sub-channel is referred to as "active".Referring to FIG. 2, sense quantum channel is shown
The quantum state of
Referring to fig. 3, a
Applying series of joint qubit-qubit unitary operations, as shown in FIG. 2. which unitary operation is applied in the first round (by
Representing) based on the most recent detection result of theAny arbitrary quantum channel can be constructed and effectively implemented using
Before describing the details of how to generate sense quantum channels according to embodiments, a simplified example of a simple case with a tree depth of L ═ 1 is described, which corresponds to a quantum channel with a Kraus rank less than 20And K1. In this case, the quantum circuit of fig. 2 is simplified to the following steps: (1) initializing
The joint unitary operation U can be represented by a 2d × 2d matrix as follows:
wherein the content of the first and second substances,<0|U|0>=K0and<1|U|0>=K1are all d × d sub-matrices and the asterisks (×) indicate other sub-matrices that are not relevant in case U is unitary. Thus, the left column of matrix U in equation 7 is a 2d × d matrix, which is isomorphic (isomorphism), meaning that the following condition is satisfied:
the isomorphic condition of equation 7 is guaranteed by the apodization property of the CPTP mapping. When the
As described below, if the
Having thus described a simplified implementation of constructing an
As discussed above in connection with fig. 2, the ith unitary operation consists of
Represents and is compared with node b of a binary tree(l)=(b1b2…bL)∈{0,1}l) And (c) correlating, wherein L is 0. For L1, forThere are only unitary operations, which areAs determined by equation 7 above, unitary is determined in a manner similar to equation 7
In the auxiliary state always in the ground state |0>In the first embodiment, a d × d sub-matrix is specified
It suffices, wherein | bl+1>Is directed to bl+1The projected measurement state of the auxiliary qubit of 0, 1. Each leaf b of the binary tree(L)∈{0,1}LWith Kraus operator marked in binary representationWherein i ═ (b)1b2…bL) +1 andIn embodiments, the dxd sub-matrixThe following can be constructed from the known Kraus operator represented by the minimum Kraus. For each node b with L-1(l)The non-negative Hermite matrix is determined and diagonalized as follows:
wherein the content of the first and second substances,
is a unitary matrix of the matrix,is a diagonal matrix with non-negative elements, anIs to satisfyThe hermitian matrix of. For ease of labelling, the matrix is arrangedSubstituted and defined as:
wherein sgn (0) is defined as zero, so thatAnd
matrix arrayIs defined as an orthogonal projectionAnd associated projectionThe correlated projectionIs defined as
Further, the inverse matrix is defined as:
in addition, the matrix
Moore-Penrose pseudo-inverse ofIs defined as:
finally, for l ═ 0, the following values are fixed:
andbased on the above definitions and relationships, the explicit expression of the correlation sub-matrix of the unitary matrix is for L0.
Wherein, b(l+1)=(b(l),b(l+1)) And for L ═ L-1 is
Therefore, the unitary matrix can be completely determined based on equations 15 and 16 using the various definitions described above
And isIs to ensure that the equidistant condition is satisfiedIs used to generate the unitary matrix. Since each of equations 15 and 16 can be determined from the Kraus operator represented by the minimum Kraus, each unitary operation required to construct quantum circuits and binary trees similar to the examples shown in fig. 2 and 3 can be determined from the Kraus operator represented by the minimum Kraus. Note that for L ═ 1, the above equation reduces to:
which is the result of for the quantum channel with
FIG. 4 depicts a
In embodiments, the
At
In some embodiments, the
If so, the
Circuit QED-based implementation
The top section describes how series of unitary operations and measurements can be used to create arbitrary quantum channels (i.e., CPTP maps), where the unitary operations used are adaptively controlled based on the detection results from the measurements.
Referring to FIG. 5, an exemplary cQED-based quantum information system 500 includes a storage cavity 510 and a transmon qubit 520 dispersively coupled from . the storage cavity 510 may be a stripline cavity or a three-dimensional cavity. the storage cavity 510 supports electromagnetic radiation, such as microwave radiation, to produce a quantum oscillator. a predetermined number d of photon number states of the quantum oscillator stored within the storage cavity 510 is used to implement the
The operation between the storage cavity 510 and the transmon qubit 520 may be used to perform entanglement operations between the two quantum systems. These operations may be implemented using drive signals generated by an electromagnetic pulse generator 550 controlled by the controller 540.
The quantum information system includes a readout cavity 532 also coupled to a transmon qubit 520. operations between readout cavity 532 and transmon qubit 510 may map the quantum states of the transmon qubits to the states of a quantum oscillator within readout cavity 532. these operations may be controlled by controller 540 controlling drive signals that control operations performed on the readout cavity and transmon qubit 520. in operation, readout cavity 532 may operate as a fast "readout" oscillator while storage cavity 510 may operate as a "storage" oscillator. in embodiments, readout cavity 532 may have a shorter decay time (and lower quality factor) than storage cavity 510. when using cavity state detector 534 to detect the state of the readout oscillator, the state of storage cavity 510 remains unmeasured.a measurement is passed from transmon qubit 520 to readout cavity 532, then using the quantum state detector of readout cavity, which may be used to detect the state of storage cavity 510. by passing quantum state information from transmon qubit 520 to readout cavity 532, storage cavity 510 may be used to determine the state of storage cavity 520 in a manner known as a measurement of storage cavity 520. this state detector may be used to determine the state of storage cavity 520.
In embodiments, the electromagnetic drive pulses generated by the electromagnetic pulse generator 550 are used to implement unitary operation on the quantum states of the quantum oscillator and the transmon qubit 520 stored in the storage cavity 510.
According to , the joint qubit-qubit system of quantum information system 500 (e.g., the joint system of a quantum oscillator with transmon qubit 520) may be described using the following Hamiltonian (Hamiltonian):
wherein higher is omittedThe term of the order. In formula 18,. omega.qIs the ground state | g of the transmon qubit 520>(sometimes referred to as | 0)>) And excited state | e>(sometimes referred to as | 1)>) Qubit transition frequency in between; omegacIs the resonant frequency of the cavity; χ is the dispersion coupling constant between the transmon qubit 520 and the oscillator;
andrespectively, a creation operator and an annihilation operator for photons within the storage chamber 510. As a result of the dispersive coupling, the qubit transition frequency changes χ when a photon is added to the cavity. Thus, the drive signal may be passed at a frequency ωq+ n χ drives the transmon qubit 520 (i.e., by applying an electromagnetic pulse to the transmon qubit 520) to modify a particular Fock state | n of the oscillator>According to embodiments, such a drive signal can modify the Fock state | n by changing the phase of the state>。By way of illustrative but non-limiting example, the transmon qubit 520 may have a transition frequency ω between 5GHz and 10GHz (such as between 7GHz and 8GHz, or about 7.6GHz)q(ii) a The quantum mechanical oscillator may have a transition frequency ω between 6GHz and 11GHz, such as between 8GHz and 9GHz or about 8.2GHzcThe dispersion shift χ may be between 1MHz and 10MHz, such as between 4MHz and 9MHz, or such as about 8.2MHz in embodiments, the dispersion shift χ may be three orders of magnitude greater than the dissipation of the transmon qubit 520 and the storage cavity 510, which allows for greater unitary control of the combined system.
FIG. 5 depicts an illustrative frequency spectrum 500 of a transmon qubit coupled to a quantum oscillator according to embodiments As described above, dispersive coupling between a physical qubit and a quantum mechanical oscillator causes the number state | n > of the oscillator to be decomposed into different frequencies of the transmon qubit.
FIG. 6 is a plan view ofExample of a qubit spectrum 600 for qubits dispersively coupled to a resonant cavity having an average photon number
The horizontal axis of the graph represents the shift in qubit transition frequency for exciting different Fock states of the coupled resonator. In other words, the figure illustrates that the transition frequency of a transmon qubit depends on the number of photons within the cavity.In the example spectrum 600 of FIG. 5, the different Fock states of the oscillator |0>, |1>, |2, |3>, |4> and |5> are each associated with a different transition frequency of the transmon qubit for example, the transition frequency of a qubit for which no photon is present in the cavity is defined as a detuning of 0MHz (and equal to the surface qubit transition frequency, which as described above can be between 5GHz and 10GHz in embodiments.) when the cavity includes a single photon, the transition frequency of a qubit is detuned by about 10MHz, when the cavity includes two photons, the transition frequency of a qubit is detuned by about 17MHz, when the cavity includes three photons, the transition frequency of a qubit is detuned by about 26MHz, when the cavity includes four photons, the transition frequency of a qubit is detuned by about 34MHz, and when the cavity includes five photons, the transition frequency of a qubit is detuned by about 43 MHz.
FIG. 7 depicts an energy level diagram 700 for a combined system including a transmon qubit 520 dispersively coupled to a storage cavity 510 based on this amount-dependent detuning of the transition frequency of the transmon qubit 520, the qubit can be selectively addressed using drive pulses that are narrow in spectral width and whose center frequency is tuned to match the transition frequency that is detuned for a particular number of excitations.
In some embodiments, the transmon qubit 520 may be driven independently of the storage cavity 510, causing a rotation of the quantum states of the transmon qubit 520. the amount of rotation of the quantum states may depend on the quantum states of the storage cavity 510 (e.g., the rotation may be photon-number dependent). such a rotation induces a photon-number dependent belie phase to the quantum states of the transmon qubit 520 while leaving the transmon states unmodified. different phases θ are shown qualitatively in FIG. 6iThis type OF operation is referred to as Selective Number-dependent Arbitrary Phase (SNAP) operation and is described in detail in U.S. patent application No. 15/552,998 entitled "TECHNIQUES OF OSCILLATOR CONTROL FOR QUANTUM INFORMATION PROCES AND RELATED SYSTEMS AND METHOD" and filed on 2017, 8/23, the entire contents OF which are incorporated herein by reference FOR at least the purpose OF enabling the discussion OF SNAP (in the event that any term used herein conflicts with the use OF that term in U.S. patent application No. 15/552,998, that term should be given a meaning that most consistent with the use herein as understood by a skilled artisan.)
In embodiments, SNAP can be used to implement the following entangled unitary operations:
wherein, Yn≡-i|g,n><e, n | + H.c. is the Pauli Y operator for the two-dimensional subspace associated with n photons in the storage cavity 510, H.c. represents the Hermite conjugate, and d is the use of quantumThe d-level of the oscillator is used to physically implement the dimensionality of the quantum digital bits. Entanglement operation UentAnd the quantum channel { S ] described by the Kraus operator0,S1Are associated. Related entanglement operation U'entCan be operated by first utilizing unitary
Acting solely on the qubit (e.g. storage chamber 510) and executing UentFollowed by separately performing an adaptive unitary operation W on the storage chamber 5100Or W1Wherein a unitary operation W0Or W1Depending on the detection results from previous measurements of the transmon qubit 520. Thus:
the decomposition of equation 20 is called "cosine-sine decomposition" and matches the two sub-matrices of the correlation of the desired unitary operation:
wherein the content of the first and second substances,
and isBased on this, a quantum circuit similar to that of fig. 2 for the sense quantum channel in cQED can be identified for different rounds of unitary operationMatrix W of0、S0、W1、S1And V. In this manner, a potentially complex joint unitary operation (e.g., of fig. 2)) Become three simplerSingle unitary operation-two unitary operations acting only on the oscillator and unitary operations acting only on the transmon qubit 520.In embodiments, the entangled unitary operation U 'is determined in the following manner'ent. First, singular value decomposition is determined
Andwhere the W matrix and the S matrix are set to their desired values based on equation 20. Then, V is ensured0=V1To decompose exclusively at , embodiments may require singular values of S0In descending order such that (S)0)j,j≥(S0)j+1,J+1And S is1Are arranged in ascending order such that (S)1)j,j≤(S1)j+1,j+1. Condition of equal distanceEnsure thatDue to the fact thatAndboth are diagonals of the element in ascending order, and soMust be the same, which means V0=V1V. Thus, obtain and satisfyAndu's'entAll of the components of (a).In the case of quantum circuits, the techniques described herein for cQED systems reduce the complex 2 d-dimensional unitary operation to two unitary operations, i.e., an entanglement operation and a measurement, that act separately on the quantum digits (e.g., quantum oscillators), where the unitary operation used may be based on the detection results from the measurement.
Computer and software aspects
In embodiments, at least non-transitory storage media are encoded with executable instructions that when executed by at least processors cause at least processors to perform a method of creating 0-sense quantum channels in
The
The
For example,
FIG. 9 depicts an
The indication may be input using a user interface, for example, the user may input the indication via a user interface, alternatively, the indication may be received from a different computer system via a network interface, in embodiments the indication may be sets of Kraus operators associated with the desired quantum channel, in another embodiment the indication may be a super operator matrix, a Choi matrix, or a Jamiolkowski matrix.
At
As described above, in embodiments, each node of the binary tree structure is associated with a respective unitary joint operation of a plurality of unitary joint operations, and each leaf of the binary tree structure is associated with a Kraus operator represented by a minimum Kraus of a desired quantum channel.
At
At
Example applications
The -sense quantum channels (i.e., CPTP maps) described in this application may include a variety of physical operations including cooling, quantum , measurement and dissipation dynamics (discrete dynamics). the ability to construct arbitrary CPTP maps provides a method of system for many aspects of quantum technology.
The application of to construct sense quantum channels is the initialization and/or stabilization of the quantum states of the quantum digits many quantum information processing tasks require working with well-defined (usually pure) initial states common methods are to cool the system to the ground state quiescently by coupling to a cold bath (cold bath) or optically pumping to a specific dark state and then performing a unitary operation to cool the system to the ground state to bring it to the desired initial state.
Quantum tubeRoad
The quantum state of the quantum digit is stabilized at the target state sigma. If the target state has a diagonal representation sigma ═ sigmaμλμ|ψμ><ψμL, where λμIs more than or equal to 0 and sigmaμλμ1, forms of the Kraus operator representing a stabilized quantum channel areWherein, | i>In contrast to the conventional approach discussed in the previous paragraph , the dissipation map bundles the cooling and state preparation steps and pumps any state to the target state σ.A second application of the -sense quantum channel construction techniques described herein is in Quantum Error Correction (QEC). in this application, multiple stable quantum states or even stable subspace may be stabilized.A plurality of quantum states may be used to encode useful classical or quantum information.in embodiments, a stable subspace using QECs may include a recovery map that implements QECs.
For having NsA qubit based stabilizer code for a stabilizer generator, the recovery being of Kraus rank
, all N may be measured sequentially using the ancillary qubitssA stabilizer generator extracts the syndrome and finally performs a correcting unitary operation conditioned on the syndrome pattern. Since the stabilizer generators are swapped with each other, their ordering does not change the syndrome. Furthermore, the stabilizer measurement need not be conditioned on previous measurements, since the unitary operation of the l-th round is only:
wherein the content of the first and second substances,
for the first stabilizer, run in the monthIndependent of previous measurement results b(l-1). Finally, with the syndromeConditional on performing corrective unitary operationsIn embodiments, QEC codes that satisfy quantum error correction conditions associated with sets of error operations can be used for which Kraus representations of QEC recovery maps can be obtained and efficiently implemented using the construction of -sense quantum channels described herein.
For a small loss probability γ per shot, the coding scheme can correct up to O (γ)2) Which includes the following four correlation processes: identifying evolution
Discard excitationsDiscarding two excitationsAnd reaction induced dephasingBased on Kraus representation of QEC recovery (Kraus rank 4), the following sets of unitary operations were obtainedFor constructing a QEC recovery channel with white-adapted quantum circuits:
wherein the projection is defined as
Andand for sigma ═ ↓, unitary operator(wherein, ) Will error the stateTransition back to | Wσ>. In other words:
wherein, U⊥, the first two rounds of projection measurements are performed to extract the error syndrome, in the last rounds, a corrective unitary operation is applied to restore the logical state(2)If (0, 0), there is no error and the operation is identified
It is sufficient. If b is(2)With (0, 1), there is a counter-effect induced dephasing error that changes the coefficients of the Fock state, so we need to useThis is corrected. If b is(2)If (1, 1), then there is a single excitation loss, which can be usedTo make the correction. If b is(2)If (1, 0), then there are two excitation losses, which can be usedTo make a full correction. Repeatedly applying the QEC to restore the channel can be performed at the point of time of the channel from | W↑>And | W↓>The system is stabilized in the spanned code space. Note that for more complex QEC codes (e.g., GKP code [ GKP _ PRA _2001 ]]) And QEC.For an approximated QEC code, analytically obtaining an optimal QEC recovery map is challenging, but a semi-deterministic plan may be used to numerically optimize the entanglement fidelity and obtain an optimal QEC recovery map.
In another application of the techniques described herein, if the intermediate measurements are part of of the output, along with the state of the quantum system, the construction of the quantum channel can be further expanded , which results in an interesting class of quantum channels called Quantum Instruments (QI).
Wherein, | mu><μ | is the orthogonal projection of the measuring device with M classical results, εμIs a full positive non-incremental mapping, andthe traces are preserved. Note thatμ(ρ) gives the measured state associated with the result μ.
In embodiments, QI is implemented as follows (1) for J1, 2μTo find epsilonμ(ρ) with Kraus operator Kμ,jMinimum Kraus representation of ( each with rank J)μ). (2) Introducing these Kraus operators
Wherein the length of the binary label is L ═ L1+L2Wherein, the frontTo encode mu, and the remaining previous onesBit to encode j (padded with zero operator so that there is always 2 in total)LOne Kraus operator). (3) Quantum circuits with L-round adaptive evolution and auxiliary measurements are used. (4) Final state of output quantity subsystem and encoding mu associated with M possible classical resultsIn this way, any QI. described in configuration 25 was constructed in embodiments, QI was used to achieve complex condition evolution of the system in embodiments QI was used for quantum information processing tasks that require measurement and adaptive control.In such embodiments, the constructed quantum channel is actually a Positive Operator Value Measure (POVM), also known as sense quantum measurement.
It is characterized by groups of hermitian semideterminants
Which adds to the identifier in embodiments, positive half piμIs decomposed into sets of Kraus operatorsIs/are as followsThus, in embodiments, the quantum circuit of the quantum instrument also implements POVM if the qubit state is removed from the QI output, in embodiments, this reduces the binary tree construction scheme of POVM.In some embodiments, POVM is used for quantum state discrimination any detector may not perfectly discriminate sets of non-orthogonal quantum states however, an optimal detector may achieve a so-called Hellstrom boundary by properly designing the POVM to optimize discrimination between the non-orthogonal states.
Summarizing the above application, there are three different classifications of CPTP mappings based on the output of the mappings, shown in FIG. 10 (a)
Other considerations
Having thus described several aspects of at least embodiments of the invention, it is to be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art, which alterations, modifications, and improvements are intended to be part of this disclosure , and are intended to be within the spirit and scope of the invention.
Various aspects of the present invention may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings, for example, aspects described in the embodiments may be combined in any manner with aspects described in other embodiments.
The use of ordinal terms such as "," "second," "third," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of claim elements over another claim element or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish claim elements having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.
All definitions, as defined and used herein, should be understood to control dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.
The indefinite articles " (" a "and" an ") as used herein in this specification and the claims are to be understood as meaning" at least "unless expressly indicated to the contrary.
As used herein in the specification and claims, the phrase "at least ," when referring to a list of or more elements, is understood to mean at least elements selected from any or more elements in the list of elements, without specifying at least of every elements specifically listed in the list of elements and without excluding any combination of elements in the list of elements.
As used herein in the specification and claims, the phrase "equal" or "the same" when referring to two values (e.g., distance, width, etc.) means that the two values are the same within manufacturing tolerances. Thus, two values being equal or identical may mean that the two values differ from each other by ± 5%.
As used herein in the specification and claims, the phrase "and/or" should be understood to mean "any or two" of the elements so joined (i.e., " or more" of the elements so joined.) the use of "and/or" listing of a plurality of elements should be interpreted in the same manner (i.e., " or more" of the elements so joined).
As used herein in the specification and claims, "or" should be understood to have the same meaning as "and/or" as defined above, "or" and/or "should be interpreted as inclusive, i.e., containing more than elements of at least , but also including more than elements of the multiple or lists, and optionally other unlisted items, when separating items in a list, terms such as" only "or" exactly "that are only explicitly indicated to the contrary, or" consisting of "when used in a claim, such as" consisting of "would mean elements of the multiple or lists , whereas terms used herein" or "in the immediate field such as" , "," " only" or "539" should be interpreted as indicating only exclusive when used in the general sense of "," but not be interpreted as having the meaning of "," or "as used in the general term" .
Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including" and "comprising" or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
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