Enhanced Framework of Quantum Approximate Optimization Algorithm and Its Parameter Setting Strategy

Quantum-enhanced radiometry via approximate quantum error correction

By exploiting the exotic quantum states of a probe, it is possible to realize efficient sensors that are attractive for practical metrology applications and fundamental studies. Similar to other quantum technologies, quantum sensing is suffering from noises and thus the experimental developments are hindered. Although theoretical schemes based on quantum error correction (QEC) have been proposed to combat noises, their demonstrations are prevented by the stringent experimental requirements, such as perfect quantum operations and the orthogonal condition between the sensing interaction Hamilton…

利用非平衡动力学实验实现临界增强型全局量子传感

Experimental Realization of Criticality-Enhanced Global Quantum Sensing via Non-Equilibrium Dynamics

针对量子临界传感的临界慢化、区间受限问题，提出结合受扰伊辛模型非平衡动力学与自适应策略的方案，在超导处理器上验证其达海森堡标度且可实现全局量子传感。

Entanglement-Enhanced Classical Communication over a Noisy Classical Channel

We present and experimentally demonstrate a communication protocol that employs shared entanglement to reduce errors when sending a bit over a particular noisy classical channel. Specifically, it is shown that, given a single use of this channel, one can transmit a bit with higher success probability when sender and receiver share entanglement compared to the best possible strategy when they do not. The experiment is realized using polarization-entangled photon pairs, whose quantum correlations play a critical role in both the encoding and decoding of the classical message. Experimentally, we …

Classical Communication Enhanced Quantum State Verification

Quantum state verification provides an efficient approach to characterize the reliability of quantum devices for generating certain target states. The figure of merit of a specific strategy is the estimated infidelity $ε$ of the tested state to the target state, given a certain number of performed measurements n. Entangled measurements constitute the globally optimal strategy and achieve the scaling that εis inversely proportional to n. Recent advances show that it is possible to achieve the same scaling simply with non-adaptive local measurements, however, the performance is still worse than …

受挫伊辛模型上的增强量子行为：量子近似优化算法研究

Enhanced Quantum behavior on frustrated Ising model: Quantum Approximate Optimization Algorithm study

本研究用QAOA定量评估二维方格受挫伊辛模型的量子效应，发现弱阻挫区激发态罕见，而量子相变点附近激发态频繁出现，凸显量子涨落增强。

Ultimate limits of approximate unambiguous discrimination

Quantum hypothesis testing is an important tool for quantum information processing. Two main strategies have been widely adopted: in a minimum error discrimination strategy, the average error probability is minimized; while in an unambiguous discrimination strategy, an inconclusive decision (abstention) is allowed to vanish any possibility of errors when a conclusive result is obtained. In both scenarios, the testing between quantum states are relatively well-understood, for example, the ultimate limits of the performance are established decades ago; however, the testing between quantum channe…

利用腔增强SPDC源改进频率复用量子中继器的纠缠生成率

Improvement of entanglement generation rate in frequency-multiplexed quantum repeaters using cavity-enhanced SPDC source

本文研究了基于cSPDC的频率复用量子中继器，通过推导频率复用光子的量子态表达式，计算了单光子干涉方案中纠缠生成的 heralding 概率和保真度，证明了在100模式复用下，25公里距离的 heralding 概率可提高至98%。

Training the Quantum Approximate Optimization Algorithm without access to a Quantum Processing Unit

In this paper, we eliminate the classical outer learning loop of the Quantum Approximate Optimization Algorithm (QAOA) and present a strategy to find good parameters for QAOA based on topological arguments of the problem graph and tensor network techniques. Starting from the observation of the concentration of control parameters of QAOA, we find a way to classically infer parameters which scales polynomially in the number of qubits and exponentially with the depth of the circuit. Using this strategy, the quantum processing unit (QPU) is only needed to infer the final state of QAOA. This method…

Entanglement of approximate quantum strategies in XOR games

We show that for any $\varepsilon>0$ there is an XOR game $G=G(\varepsilon)$ with $Θ(\varepsilon^{-1/5})$ inputs for one player and $Θ(\varepsilon^{-2/5})$ inputs for the other player such that $Ω(\varepsilon^{-1/5})$ ebits are required for any strategy achieving bias that is at least a multiplicative factor $(1-\varepsilon)$ from optimal. This gives an exponential improvement in both the number of inputs or outputs and the noise tolerance of any previously-known self-test for highly entangled states. Up to the exponent $-1/5$ the scaling of our bound with $\varepsilon$ is tight: for any XOR g…

Optimized Bose-Einstein-condensate production in a dipole trap based on a 1070-nm multifrequency laser: Influence of enhanced two-body loss on the evaporation process

We present an optimized strategy for the production of tightly confined Bose-Einstein condensates (BEC) of 87Rb in a crossed dipole trap with direct loading from a magneto-optical trap. The dipole trap is created with light of a multifrequency fiber laser with a center wavelength of 1070nm. Evaporative cooling is performed by ramping down the laser power only. A comparison of the resulting atom number in an almost pure BEC to the initial atom number and the value for the gain in phase space density per atom lost confirm that this straightforward strategy is very efficient. We observe that the …

量子近似优化算法与量子增强马尔可夫链蒙特卡洛：4DVAR数据同化的一种混合方法

Quantum Approximate Optimization Algorithm and Quantum-enhanced Markov Chain Monte Carlo: A Hybrid Approach to Data Assimilation in 4DVAR

提出混合量子-经典框架QVPF，结合QAOA与QMCMC优化变分粒子滤波器，以解决4DVAR在高维非线性系统中的计算挑战，显著提升数据同化的准确性与效率。

Quantum symmetry from enhanced sampling methods

We address the problem of the minus sign sampling for two electron systems using the path integral approach. We show that this problem can be reexpressed as one of computing free energy differences and sampling the tails of statistical distributions. Using Metadynamics, a realistic problem like that of two electrons confined in a quantum dot can be solved. We believe that this is a strategy that can possibly be extended to more complex systems.

A synchronous game for binary constraint systems

Recently, W. Slofstra proved that the set of quantum correlations is not closed. We prove that the set of synchronous quantum correlations is not closed, which implies his result, by giving an example of a synchronous game that has a perfect quantum approximate strategy but no perfect quantum strategy. We also exhibit a graph for which the quantum independence number and the quantum approximate independence number are different. We prove new characterisations of synchronous quantum approximate correlations and synchronous quantum spatial correlations. We solve the synchronous approximation pro…