相位差的两步优化测量

Quantum enhanced spectroscopy with entangled multi-photon states

Traditionally, spectroscopy is performed by examining the position of absorption lines. However, at frequencies near the transition frequency, additional information can be obtained from the phase shift. In this work we consider the information about the transition frequency obtained from both the absorption and the phase shift, as quantified by the Fisher information in an interferometric measurement. We examine the use of multiple single-photon states, NOON states, and numerically optimized states that are entangled and have multiple photons. We find the optimized states that improve over th…

Fidelity-optimized quantum state estimation

We describe an optimized, self-correcting procedure for the Bayesian inference of pure quantum states. By analyzing the history of measurement outcomes at each step, the procedure returns the most likely pure state, as well as the optimal basis for the measurement that is to follow. The latter is chosen to maximize, on average, the fidelity of the most likely state after the measurement. We also consider a practical variant of this protocol, where the available measurement bases are restricted to certain limited sets of bases. We demonstrate the success of our method by considering in detail t…

Randomizing Quantum Walk

The evolution of a walker in standard "Discrete-time Quantum Walk (DTQW)" is determined by coin and shift unitary operators. The conditional shift operator shifts the position of the walker to right or left by unit step size while the direction of motion is specified by the coin operator. This scenario can be generalized by choosing the step size randomly at each step in some specific interval. For example, the value of the roll of a dice can be used to specify the step size after throwing the coin. Let us call such a quantum walk "Discrete-time Random Step Quantum Walk (DTRSQW)". A completely…

Optimized geometries for future generation optical lattice clocks

Atoms deeply trapped in magic wavelength optical lattices provide a Doppler- and collision-free dense ensemble of quantum emitters ideal for high precision spectroscopy. Thus, they are the basis of some of the best optical clock setups to date. However, despite their minute optical dipole moments the inherent long range dipole-dipole interactions in such lattices generate line shifts, dephasing and modified decay. We show that in a perfectly filled lattice these effects are resonantly enhanced depending on lattice constant, lattice geometry and excitation scheme inducing clock shifts of many a…

量子光学非线性位移门单模运转的影响

Efficiencies for the single mode operation of a quantum optical nonlinear shift gate

研究了一维自由空间中由单个二能级原子实现的量子光学非线性π相移门的单模运转。由于在原子处的相互作用中，输入光子的单模特性不被保留，我们分析了仍然可以实现的单模操作的效率。我们展示了如何优化输入脉冲形状，以获得高效率的非线性单模操作。通过这种分析，我们获得了成功的非线性π相移操作的最佳单模透射率为78%。

Implementation of a single-shot receiver for quaternary phase-shift keyed coherent states

We experimentally investigate a strategy to discriminate between quaternary phase-shift keyed coherent states based on single-shot measurements that is compatible with high-bandwidth communications. We extend previous theoretical work in single-shot measurements to include critical experimental parameters affecting the performance of practical implementations. Specifically, we investigate how the visibility of the optical displacement operations required in the strategy impacts the achievable discrimination error probability, and identify the experimental requirements to outperform an ideal he…

通用双量子比特门的优化设计

Optimized design of universal two-qubit gates

我们构建了CNOT和其他通用双量子位门的优化实现，与许多先前提出的协议不同，这些实现是在一个步骤中进行的。新协议需要可调的量子位间耦合，但作为回报，门操作的质量有了显着的改善。我们的优化过程可以进一步扩展到基本的双量子比特以及不可约的多量子比特门的组合。

A new quantum algorithm for the hidden shift problem in $\mathbb{Z}_{2^t}^n$

In this paper we make a step towards a time and space efficient algorithm for the hidden shift problem for groups of the form $\mathbb{Z}_k^n$. We give a solution to the case when $k$ is a power of 2, which has polynomial running time in $n$, and only uses quadratic classical, and linear quantum space in $n\log (k)$. It can be a useful tool in the general case of the hidden shift and hidden subgroup problems too, since one of the main algorithms made to solve them can use this algorithm as a subroutine in its recursive steps, making it more efficient in some instances.

Hamiltonian extensions in quantum metrology

We study very generally to what extent the uncertainty with which a phase shift can be estimated in quantum metrology can be reduced by extending the Hamiltonian that generates the phase shift to an ancilla system with a Hilbert space of arbitrary dimension, and allowing arbitrary interactions between the original system and the ancilla. Such Hamiltonian extensions provide a general framework for open quantum systems, as well as for "non-linear metrology schemes" that have been investigated over the last few years. We prove that such Hamiltonian extensions cannot improve the sensitivity of the…

相对论电子的散射及其与光学现象的类比：阶跃势下纵向与横向位移的研究

Scattering of relativistic electrons and analogies with optical phenomena: A study of longitudinal and transverse shifts at step potentials

本文通过光学类比研究相对论电子在势阶处的散射，利用狄拉克流守恒和总角动量守恒阐明古斯-汉欣纵向位移与伊姆伯特-费多罗夫横向位移的物理机制，并揭示其与自旋霍尔效应的联系及在狄拉克和拓扑材料器件中的应用潜力。

Optimized Quantum Circuit Partitioning

The main objective of this paper is to improve the communication costs in distributed quantum circuits. To this end, we present a method for generating distributed quantum circuits from monolithic quantum circuits in such a way that communication between partitions of a distributed quantum circuit is minimized. Thus, the communication between distributed components is performed at a lower cost. Compared to existing works, our approach can effectively map a quantum circuit into an appropriate number of distributed components. Since teleportation is usually the protocol used to connect component…