Components for Optical Qubits in the Radio Frequency Basis

Reduced randomness in quantum cryptography with sequences of qubits encoded in the same basis

We consider the cloning of sequences of qubits prepared in the states used in the BB84 or 6-state quantum cryptography protocol, and show that the single-qubit fidelity is unaffected even if entire sequences of qubits are prepared in the same basis. This result is of great importance for practical quantum cryptosystems because it reduces the need for high-speed random number generation without impairing on the security against finite-size attacks.

Effective Hamiltonians for interacting superconducting qubits -- local basis reduction and the Schrieffer-Wolff transformation

An open question in designing superconducting quantum circuits is how best to reduce the full circuit Hamiltonian which describes their dynamics to an effective two-level qubit Hamiltonian which is appropriate for manipulation of quantum information. Despite advances in numerical methods to simulate the spectral properties of multi-element superconducting circuits, the literature lacks a consistent and effective method of determining the effective qubit Hamiltonian. Here we address this problem by introducing a novel local basis reduction method. This method does not require any ad hoc assumpt…

Symmetric functions of qubits in an unknown basis

Consider an n qubit computational basis state corresponding to a bit string x, which has had an unknown local unitary applied to each qubit, and whose qubits have been reordered by an unknown permutation. We show that, given such a state with Hamming weight |x| at most n/2, it is possible to reconstruct |x| with success probability 1 - |x|/(n-|x|+1), and thus to compute any symmetric function of x. We give explicit algorithms for computing whether or not |x| is at least t for some t, and for computing the parity of x, and show that these are essentially optimal. These results can be seen as ge…

Quantum Microwave Radiometry with a Superconducting Qubit

The interaction of photons and coherent quantum systems can be employed to detect electromagnetic radiation with remarkable sensitivity. We introduce a quantum radiometer based on the photon-induced-dephasing process of a superconducting qubit for sensing microwave radiation at the sub-unit-photon level. Using this radiometer, we demonstrated the radiative cooling of a 1-K microwave resonator and measured its mode temperature with an uncertainty ~0.01 K. We have thus developed a precise tool for studying the thermodynamics of quantum microwave circuits, which provides new solutions for calibra…

Efficient Decomposition of Single-Qubit Gates into $V$ Basis Circuits

We develop the first constructive algorithms for compiling single-qubit unitary gates into circuits over the universal $V$ basis. The $V$ basis is an alternative universal basis to the more commonly studied $\{H,T\}$ basis. We propose two classical algorithms for quantum circuit compilation: the first algorithm has expected polynomial time (in precision $\log(1/ε)$) and offers a depth/precision guarantee that improves upon state-of-the-art methods for compiling into the $\{H,T\}$ basis by factors ranging from 1.86 to $\log_2(5)$. The second algorithm is analogous to direct search and yields ci…

Mismatched-basis statistics enable quantum key distribution with uncharacterized qubit sources

In the postprocessing of quantum key distribution, the raw key bits from the mismatched-basis measurements, where two parties use different bases, are normally discarded. Here, we propose a postprocessing method that exploits measurement statistics from mismatched-basis cases, and prove that incorporating these statistics enables uncharacterized qubit sources to be used in the measurement-device-independent quantum key distribution protocol and the Bennett-Brassard 1984 protocol, a case which is otherwise impossible.

What is measured when a qubit measurement is performed on a multi-qubit chip?

We study how single-qubit dispersive readout works alongside two qubit coupling. To make calculations analytically tractable, we use a simplified model which retains core characteristics of but is discretised compared to dispersive homodyne detection. We show how measurement speed and power determine what information about the qubit(s) is accessed. Specifically we find the basis the measurement is closest to projecting onto. Compared to the basis gates are applied in, this measurement basis is modified by the presence of photons in the readout resonator.

Symplectic space and orthogonal space of n qubits

In the Hilbert space of n qubits, we introduce the symplectic space (n odd) and the orthogonal space (n even) via the spin-flip operator. Under this mathematical structure we discuss some properties of n qubits, including homomorphically mapping the local operations of n qubits into the symplectic group or orthogonal group, and prove that the generalized ``magic basis'' is just the bi-orthonormal basis (that is, the orthonormal basis of both Hilbert space and the orthogonal space ). Finally, an example is given to discuss the application in physics of this mathematical structure.

A simple scheme of teleportation of arbitrary multipartite qubit entanglement

In this paper, we define a cross product operator and construct the cross Bell basis, by use this basis and Bell measurements we give a simple scheme of the teleportation of arbitrary multipartite qubit entanglement.

Peculiarities of qubit initial-state preparation by nonselective measurements on an overcomplete basis

We consider the qubit initial state preparation due to the nonselective measurements on an overcomplete basis, when the number of outcomes $N=3$. To be specific, we have chosen the dephasing model and applied the conditions for a post-measurement state to ensure a gradual coherence enhancement at the initial stage of the system evolution. It is shown that contrary to the von Neumann-Lüders projection scheme with $N=2$, the most mixed post-measurement state of the qubit in the general case can depend on the bath temperature. This remarkable feature allows one to consider a ``temperature control…

Reduction of circuit depth by mapping qubit-based quantum gates to a qudit basis

We present a scalable set of universal gates and multiply controlled gates in a qudit basis through a bijective mapping from N qubits to qudits with D = 2^N levels via rotations in U(2). For each of the universal gates (H, CNOT, and T), as well as the NOT gate and multiply-controlled-Z gates, we describe a systematic approach to identifying the set of U(2) rotations required to implement each gate for any qudit of size N and with minimal use of an ancilla level. The qudit gates are analyzed in terms of the total rotation count and gate depth as the system scales with D. We apply the qudit-basi…

Mutually unbiased binary observable sets on N qubits

The Pauli operators (tensor products of Pauli matrices) provide a complete basis of operators on the Hilbert space of N qubits. We prove that the set of 4^N-1 Pauli operators may be partitioned into 2^N+1 distinct subsets, each consisting of 2^N-1 internally commuting observables. Furthermore, each such partitioning defines a unique choice of 2^N+1 mutually unbiased basis sets in the N-qubit Hilbert space. Examples for 2 and 3 qubit systems are discussed with emphasis on the nature and amount of entanglement that occurs within these basis sets.

原子-光子2-qubit态的完整Bell基测量及其在量子网络中的应用

Full Bell-basis measurement of an atom-photon 2-qubit state and its application for quantum networks

本研究提出并实现了一种利用单离子量子存储器和heralded absorption区分所有四个Bell态的协议，通过光子qubit保态映射和原子到光子量子态隐形传态演示了完整Bell态投影，突破了线性光学50%的测量效率限制。

N量子比特系统最大纠缠基矢完备集的构建

Construction of the Complete Set of Maximally Entangled Basis Vectors for N-Qubit Systems

本研究提出一种随机数方法，从三量子比特系统推广至N量子比特系统，构建最大纠缠基矢及其量子电路，并统计所需单量子比特门和CNOT门数量，为量子技术应用提供理论基础和实用技术。

On the role of the basis of measurement in quantum gate teleportation

Quantum teleportation is a powerful protocol with applications in several schemes of quantum communication, quantum cryptography and quantum computing. The present work shows the required conditions for a two-qubit quantum gate to be deterministically and probabilistically teleported by a quantum gate teleportation scheme using different basis of measurement. Additionally, we present examples of teleportation of two-qubit gates that do not belong to Clifford group as well the limitations of the quantum gate teleportation scheme employing a four-qubit state with genuine four-way entanglement.

Why Two Qubits Are Special

We analyze some special properties of a system of two qubits, and in particular of the so-called Bell basis for this system, which have played an important role in recent papers on entanglement of qubits. In particular, we show which of these properties may be generalized to higher dimension. We give a general construction for bases of maximally entangled vectors in any dimension, but show that none of the properties related to complex conjugation in Bell basis can be realized for higher dimensional analogs.

Two-local qubit Hamiltonians: when are they stoquastic?

We examine the problem of determining if a 2-local Hamiltonian is stoquastic by local basis changes. We analyze this problem for two-qubit Hamiltonians, presenting some basic tools and giving a concrete example where using unitaries beyond Clifford rotations is required in order to decide stoquasticity. We report on simple results for $n$-qubit Hamiltonians with identical 2-local terms on bipartite graphs. Our most significant result is that we give an efficient algorithm to determine whether an arbitrary $n$-qubit XYZ Heisenberg Hamiltonian is stoquastic by local basis changes.

Multiparticle entanglement in graph-diagonal states: Necessary and sufficient conditions for four qubits

The characterization of genuine multiparticle entanglement is important for entanglement theory as well as experimental studies related to quantum information theory. Here, we completely characterize genuine multiparticle entanglement for four-qubit states diagonal in the cluster-state basis. In addition, we give a complete characterization of multiparticle entanglement for all five-qubit graph states mixed with white noise, for states diagonal in the basis corresponding to the five-qubit Y-shaped graph, and for a family of graph states with an arbitrary number of qubits.

光子量子比特编码互转用于异构量子网络

Photonic qubit encoding interconversion for heterogeneous quantum networking

研究提出一种将光子量子比特编码从偏振基转换到时间-bin基的协议，通过光纤传输实现纠缠分发，并展示了在异构量子网络中连接不同量子比特平台的实用方法。

Let Each Quantum Bit Choose Its Basis Gates

Near-term quantum computers are primarily limited by errors in quantum operations (or gates) between two quantum bits (or qubits). A physical machine typically provides a set of basis gates that include primitive 2-qubit (2Q) and 1-qubit (1Q) gates that can be implemented in a given technology. 2Q entangling gates, coupled with some 1Q gates, allow for universal quantum computation. In superconducting technologies, the current state of the art is to implement the same 2Q gate between every pair of qubits (typically an XX- or XY-type gate). This strict hardware uniformity requirement for 2Q gat…

Coherent Processing of a Qubit Using One Squeezed State

We use a single squeezed state to represent a qubit, which can be coherently processed in a deconvolution picture (DP) in the presence of noise. We avail ourselves of the fact that when evolution is governed by a quadratic dissipative equation, there exists a basis of squeezed states that evolves to another basis of such states in the DP. An operator acts as an impurity filter, restoring the coherence lost from the inexorable interactions of the qubit with its surroundings.

Radio frequency mixing modules for superconducting qubit room temperature control systems

As the number of qubits in nascent quantum processing units increases, the connectorized RF (radio frequency) analog circuits used in first generation experiments become exceedingly complex. The physical size, cost and electrical failure rate all become limiting factors in the extensibility of control systems. We have developed a series of compact RF mixing boards to address this challenge by integrating I/Q quadrature mixing, IF(intermediate frequency)/LO(local oscillator)/RF power level adjustments, and DC (direct current) bias fine tuning on a 40 mm $\times $ 80 mm 4-layer PCB (printed circ…

多个量子比特上的对称量子联合测量

Symmetric quantum joint measurements on multiple qubits

本文研究对称量子联合测量在多量子比特上的推广，提出利用 Bloch 球正四面体顶点态构造三量子比特测量基的方法，并将其推广至 $n$ 量子比特版本以保持对称性。

Quantum interference in timed Dicke basis and its effect on bipartite entanglement

We analyze the effect of position dependent excitation phase on the properties of entanglement between two qubits formed in atomic systems. We show that the excitation phase induces a vacuum mediated quantum interference in the system that affects the dynamical behavior of entanglement between the qubits. It is also found that the quantum interference leads to a coherent population transfer between the symmetric and antisymmetric states which can considerably modify the dynamics of two-qubit entanglement and can even prevent finite time disentanglement (sudden death) under certain conditions.

Reducing qubit requirements while maintaining numerical precision for the Variational Quantum Eigensolver: A Basis-Set-Free Approach

We present a basis-set-free approach to the variational quantum eigensolver using an adaptive representation of the spatial part of molecular wavefunctions. Our approach directly determines system-specific representations of qubit Hamiltonians while fully omitting globally defined basis sets. In this work, we use directly determined pair-natural orbitals on the level of second-order perturbation theory. This results in compact qubit Hamiltonians with high numerical accuracy. We demonstrate initial applications with compact Hamiltonians on up to 20 qubits where conventional representation would…

Orthogonal product bases of four qubits

An orthogonal product basis (OPB) of a finite-dimensional Hilbert space $H=H_1\otimes H_2\otimes\cdots\otimes H_n$ is an orthonormal basis of $H$ consisting of product vectors $x_1\otimes x_2\otimes\cdots\otimes x_n$. We show that the problem of classifying the OPBs of an $n$-qubit system can be reduced to a purely combinatorial problem. We solve this combinatorial problem in the case of four qubits and obtain 33 multiparameter families of OPBs. Each OPB of four qubits is equivalent, under local unitary operations and qubit permutations, to an OPB belonging to at least one of these families.

三叉树变换等价于Fock基的线性编码

Ternary tree transformations are equivalent to linear encodings of the Fock basis

本研究针对费米子-量子比特映射中三叉树变换与线性编码两类方法体系独立、符号不统一的问题，提出通用描述框架，证明所有保乘积的三叉树变换均等价于Fock基的线性编码，厘清了两类方法的内在关联。

通过计算基相位实现多量子比特酉算子的相互作用分解

Interaction-resolved decomposition of multi-qubit unitaries via computational-basis phases

本文引入一种通过计算基相位对角化框架对n量子比特酉算子进行相互作用分解的方法，定义支持选择性相位不变量以精确解析k体相互作用项，并用于量子最优控制合成目标相互作用。

Entangled webs: Tight bound for symmetric sharing of entanglement

Quantum entanglement cannot be unlimitedly shared among arbitrary number of qubits. Larger the number of entangled pairs in an N-qubit system, smaller the degree of bi-partite entanglement is. We analyze a system of N qubits in which an arbitrary pair of particles is entangled. We show that the maximum degree of entanglement (measured in the concurrence) between any pair of qubits is 2/N. This tight bound can be achieved when the qubits are prepared in a pure symmetric (with respect to permutations) state with just one qubit in the basis state |0> and the others in the basis state |1>.

An optimal single-electron charge qubit for solid-state double quantum dots

We report on an optimal single-electron charge qubit for a solid-state double quantum dot (DQD) system and analyse its dynamics under a time-dependent linear detuning, using GPU accelerated numerical solutions to the time-dependent Schrödinger equation. The optimal qubit is found to have basis states defined as the symmetric and antisymmetric linear combinations of the lowest energy bonding and anti-bonding states of the DQD at zero bias. In contrast to charge qubits defined by the two localised ground states of the uncoupled DQD, this choice of the basis causes the resulting dynamics to have …

Emergence of metastable pointer states basis in non-Markovian quantum dynamics

We investigate the dynamics of classical and quantum correlations between two qubits. Each qubit is implemented by a pair of phosphorous impurities embedded in a silicon substrate. The main decoherence mechanism affecting these types of qubits is provided by the coupling of the phosphorous impurities to the acoustical vibrations of the silicon lattice. We find that depending on the temperature of the substrate and the initial state, three different dynamics can be found. These are characterized by the number of abrupt changes in both classical and quantum correlations. We also show that the co…

A General Bidirectional Controlled/Uncontrolled Quantum Teleportation Protocol

In this paper, different from the other existing methods that only the special and limited numbers of qubits transmit between Alice and Bob, a general method is proposed to implement Bidirectional Quantum Controlled/uncontrolled Teleportation (BQCT/BQT) that Alice and Bob can transmit each type of arbitrary n and m-qubits to each other, simultaneously. This protocol is based on Controlled-NOT (CNOT) operation, appropriate single-qubit unitary operations and single-qubit measurement in the Z-basis and X-basis. Also, the quantum channel can be created by using Hadamard and CNOT operations. One o…

探测连续基系统的纠缠

Probing entanglement of a continuous basis system

本文提出一种仅测量可及两量子比特子系统来探测不可及连续基系统纠缠的方法，并发现纠缠再分配中的保守流状行为。

测量一个量子比特能揭示另一个的什么信息？$K$-网络作为量子电路的有向诊断

What does measuring one qubit reveal about another? $K$-networks as a directed diagnostic for quantum circuits

提出有向、基条件化的边权重 $K_{i\to j}$，用于诊断量子电路中一个量子比特测量对另一个量子比特条件状态的影响，可从两量子比特约化密度矩阵计算，并展示其在量子电路诊断中的应用。

具有相位敏感性的单量子比特测量在线性簇态中的拓扑分类

Phase-sensitive framed-ribbon representation of single-qubit Pauli measurements in linear cluster states

本研究提出了一种基于拓扑框架的相位敏感分类方法，用于描述线性簇态中单量子比特测量的拓扑特性，揭示量子相位与带框架拓扑不变量的直接关联。

Decoherence-protected memory for a single-photon qubit

The long-lived, efficient storage and retrieval of a qubit encoded on a photon is an important ingredient for future quantum networks. Although systems with intrinsically long coherence times have been demonstrated, the combination with an efficient light-matter interface remains an outstanding challenge. In fact, the coherence times of memories for photonic qubits are currently limited to a few milliseconds. Here we report on a qubit memory based on a single atom coupled to a high-finesse optical resonator. By mapping and remapping the qubit between a basis used for light-matter interfacing a…

Experimental proposal for symmetric minimal two-qubit state tomography

We propose an experiment that realizes a symmetric informationally complete (SIC) probability-operator measurement (POM) in the four-dimensional Hilbert space of a qubit pair. The qubit pair is carried by a single photon as a polarization qubit and a path qubit. The implementation of the SIC POM is accomplished with the means of linear optics. The experimental scheme exploits a new approach to SIC POMs that uses a two-step process: a measurement with full-rank outcomes, followed by a projective measurement on a basis that is chosen in accordance with the result of the first measurement. The ba…

Synchronizing the dynamics of a single NV spin qubit on a parametrically coupled radio-frequency field through microwave dressing

A hybrid spin-oscillator system in parametric interaction is experimentally emulated using a single NV spin qubit immersed in a radio frequency (RF) field and probed with a quasi resonant microwave (MW) field. We report on the MW mediated locking of the NV spin dynamics onto the RF field, appearing when the MW driven Rabi precession frequency approaches the RF frequency and for sufficiently large RF amplitudes. These signatures are analog to a phononic Mollow triplet in the MW rotating frame for the parametric interaction and promise to have impact in spin-dependent force detection strategies.

On Universal and Fault-Tolerant Quantum Computing

A novel universal and fault-tolerant basis (set of gates) for quantum computation is described. Such a set is necessary to perform quantum computation in a realistic noisy environment. The new basis consists of two single-qubit gates (Hadamard and ${σ_z}^{1/4}$), and one double-qubit gate (Controlled-NOT). Since the set consisting of Controlled-NOT and Hadamard gates is not universal, the new basis achieves universality by including only one additional elementary (in the sense that it does not include angles that are irrational multiples of $π$) single-qubit gate, and hence, is potentially the…

Charge shelving and bias spectroscopy for the readout of a charge-qubit on the basis of superposition states

Charge-based qubits have been proposed as fundamental elements for quantum computers. One commonly proposed readout device is the single-electron transistor (SET). SETs can distinguish between localized charge states, but lack the sensitivity to directly distinguish superposition states, which have greatly enhanced coherence times compared with position states. We propose introducing a third dot, and exploiting energy dependent tunnelling from the qubit into this dot (bias spectroscopy) for pseudo-spin to charge conversion and superposition basis readout. We introduce an adiabatic fast passage…

Relaxation, decoherence and steady-state population inversion in qubits doubly dressed by microwave and radiofrequency fields

The coherent dynamics of relaxing spin qubits driven by a classical bichromatic field comprising a strong resonant component and a weaker component with a frequency close to the strong-field Rabi frequency is studied. The double dressing by the bichromatic field modifies dephasing and dissipation processes. We demonstrate that detuning of the weaker-field frequency from the strong-field Rabi frequency prolongs the decay of Rabi oscillations between some doubly dressed states. The sensitivity of Rabi oscillations to the modified detuning-dependent relaxation is illustrated for nitrogen-vacancy …

Standard Quantum Teleportation of an Arbitrary N-Qubit State, Non-Existence of Magic Basis and Existence of Magic Partial Bases for 2N Entangled Qubit States with N>1

We present a simple and precise protocol for standard quantum teleportation of N-qubit state, considering the most general resource q-channel and Bell states. We find condition on these states for perfect teleportation and give explicitly the unitary transformation required to be done by Bob for achieving perfect teleportation. We discuss connection of our simple theory with the complicated related work on this subject and with character matrix, transformation, judgment and kernel operators defined in this context. We also prove that the magic basis discussed by Hill and Wootters [Phys. Rev. L…

基变换的量子速度极限

Quantum Speed Limit for Change of Basis

本文将量子速度极限推广到量子态集合，研究态基到无偏基的最快转换，给出低维紧界、多量子比特与一般 d 维界限，并分析双量子比特、qutrit 及相干性生成的最短时间。

Many-body strategies for multi-qubit gates - quantum control through Krawtchouk chain dynamics

We propose a strategy for engineering multi-qubit quantum gates. As a first step, it employs an eigengate to map states in the computational basis to eigenstates of a suitable many-body Hamiltonian. The second step employs resonant driving to enforce a transition between a single pair of eigenstates, leaving all others unchanged. The procedure is completed by mapping back to the computational basis. We demonstrate the strategy for the case of a linear array with an even number N of qubits, with specific XX+YY couplings between nearest neighbors. For this so-called Krawtchouk chain, a 2-body dr…

Optimal feedback control for the rapid preparation of a single qubit

We consider the use of feedback control during a measurement to increase the rate at which a single qubit is purified, and more generally the rate at which near-pure states may be prepared. We derive the optimal bang-bang algorithm for rapid state preparation from an initially completely mixed state when the measurement basis is unrestricted, and evaluate its performance numerically. We also consider briefly the case in which the measurement basis is fixed with respect to the state to be prepared, and describe the qualitative structure of the optimal bang-bang algorithm.

Complete Separability and Fourier representations of n-qubit states

Necessary conditions for separability are most easily expressed in the computational basis, while sufficient conditions are most conveniently expressed in the spin basis. We use the Hadamard matrix to define the relationship between these two bases and to emphasize its interpretation as a Fourier transform. We then prove a general sufficient condition for complete separability in terms of the spin coefficients and give necessary and sufficient conditions for the complete separability of a class of generalized Werner densities. As a further application of the theory, we give necessary and suffi…

The Universality of the Quantum Fourier Transform in Forming the Basis of Quantum Computing Algorithms

The quantum Fourier transform (QFT) is a powerful tool in quantum computing. The main ingredients of QFT are formed by the Walsh-Hadamard transform H and phase shifts P(.), both of which are 2x2 unitary matrices as operators on the two-dimensional 1-qubit space. In this paper, we show that H and P(.) suffice to generate the unitary group U(2) and, consequently, through controlled-U operations and their concatenations, the entire unitary group U(2^n) on n-qubits can be generated. Since any quantum computing algorithm in an n-qubit quantum computer is based on operations by matrices in U(2^n), i…

利用混合宇称与直接读出的Z基测量

Z-basis measurements using mixed parity and direct readout

本文提出利用混合宇称和直接读出，在不使用辅助读出量子比特的情况下对三量子比特自旋寄存器进行Z基测量与量子态层析，并通过仿真和GHZ态实验验证了该方法的有效性。

使用单量子比特的高效中介半量子密钥分发协议

Efficient Mediated Semi-Quantum Key Distribution Protocol Using Single Qubits

本文提出一种新的高效中介半量子密钥分发协议，通过让不可信第三方仅在X基下制备和测量量子比特，经典参与方仅在Z基下操作并执行Hadamard操作，在保持量子比特效率的同时提升实用性，并证明其安全性。

超导量子比特电荷基矢层析成像的一种方案

A proposal for charge basis tomography of superconducting qubits

该研究提出一种结合约瑟夫森能量脉冲序列与投影式电荷基矢读出的通用协议以实现超导量子电路的电荷基矢层析成像，通过模拟验证其可重构 transmon 基态并检测模型哈密顿量偏差，为检测材料相互作用及拓扑相奠定基础。

无消相干子空间基态的高效制备

Efficient Preparation of Decoherence Free Subspace Basis States

提出一种确定性方法，利用投影测量和量子电路为任意大小的qubit系统制备纯正交完整的DFS基态，并从理论与数值上分析资源成本，验证其在NISQ设备上的可实现性。

Optimal implementation of two-qubit linear optical quantum filters

We design optimal interferometric schemes for implementation of two-qubit linear optical quantum filters diagonal in the computational basis. The filtering is realized by interference of the two photons encoding the qubits in a multiport linear optical interferometer, followed by conditioning on presence of a single photon in each output port of the filter. The filter thus operates in the coincidence basis, similarly to many linear optical unitary quantum gates. Implementation of the filter with linear optics may require an additional overhead in terms of reduced overall success probability of…

基于变分基态编码器的电子-声子系统高效量子模拟

Efficient Quantum Simulation of Electron-Phonon Systems by Variational Basis State Encoder

本研究针对电子-声子系统量子模拟的编码标度问题，提出变分基态编码算法，将满足纠缠熵面积律系统的量子比特和量子门标度降至O(1)，经数值和硬件实验验证，1-2个量子比特即可覆盖强弱耦合区，推动实用量子模拟发展。

Model for monitoring of a charge qubit using a radio-frequency quantum point contact including experimental imperfections

The extension of quantum trajectory theory to incorporate realistic imperfections in the measurement of solid-state qubits is important for quantum computation, particularly for the purposes of state preparation and error-correction as well as for readout of computations. Previously this has been achieved for low-frequency (dc) weak measurements. In this paper we extend realistic quantum trajectory theory to include radio frequency (rf) weak measurements where a low-transparency quantum point contact (QPC), coupled to a charge qubit, is used to damp a classical oscillator circuit. The resultin…