C. Bonato, D. Simon, P. Villoresi, A. V. Sergienko
We investigate how quantum coincidence interferometry is affected by a controllable manipulation of transverse wave-vectors in type-II parametric down conversion using adaptive optics techniques. In particular, we discuss the possibility of spatial walk-off compensation in quantum interferometry and a new effect of even-order spatial aberration cancellation.
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We propose a generalized form of entangled coherent states (ECS) and apply them in a multi-arm optical interferometer to estimate multiple phase shifts. We obtain the quantum Cramer-Rao bounds for both the linear and nonlinear parameterization protocols. Through the analysis, we find that, utilizing the simultaneous estimation, this generalized form of ECS gives a better precision than the generalized NOON states [Phys. Rev. Lett. \textbf{111}, 070403 (2013)]. Moreover, comparing with the independent estimation, both the linear and nonlinear protocols have the same advantage in the relation to…
Multiparameter estimation with an array of entangled atomic sensors
实验演示了利用纠缠原子系综阵列进行多参数量子计量，通过分裂自旋压缩系综构建可灵活配置的传感器阵列，并采用最优估计协议在多参数估计任务中显著超越标准量子极限。
Quantum multiparameter estimation with multi-mode photon catalysis entangled squeezed state
本研究提出基于Fredkin门生成多模纠缠催化压缩真空态的方法，将其用于多相位同时估计，证实可提升QCRB性能且对光子损耗鲁棒性更强，可应用于量子计量多参数估计场景。
Quantum multiparameter estimation enhanced by a topological phase transition
本文利用拓扑相变点附近量子度量张量的奇异行为，提出一种仅需基态探针的量子多参数估计协议，其性能媲美量子控制增强方法，并开发了自适应策略以逼近量子Cramér-Rao界。
Distributed quantum multiparameter estimation with optimal local measurements
本研究提出分布式MZI阵列传感器，通过局域测量实现量子多参数估计，纠缠协议以单个非经典态达到灵敏度$1/\ar{n}_T^2$，相比独立方案获得$d$倍增益，克服散粒噪声极限。
Finding the optimal probe state for multiparameter quantum metrology using conic programming
本文提出锥规划框架来确定多参数量子信道估计的最优探针态，涵盖Holevo-Nagaoka界和紧精度界，并分析了最大纠缠探针态的最优性及其在场传感问题中的应用。
We discuss the Heisenberg limit in the multiparameter metrology within two different paradigms -- the one, where the measurement is repeated many times (so the Cramér-Rao bound is guaranteed to be asymptotically saturable) and the second one, where all the resources are allocated into one experimental realization (analyzed with the mimimax approach). We investigate the potential advantage of measuring all the parameter simultaneously compared to estimating them individually, while spending the same total amount of resources. We show that in general the existence of such an advantage, its magni…
Using a quantum version of the Bell-Ziv-Zakai bound, I derive a Heisenberg limit to multiparameter estimation for any Gaussian prior probability density. The mean-square error lower bound is shown to have a universal quadratic scaling with respect to a quantum resource, such as the average photon number in the case of optical phase estimation, suitably weighted by the prior covariance matrix.
Quantum multiparameter estimation with graph states
针对 SU(2) 多参数同时估计难题，提出基于 n 量子比特图态和 SU(N) 演化的估计方案，证明其可达到量子 Cramér-Rao 界。
Precision Limits of Multiparameter Markovian-Noise Metrology
本文研究了通过马尔可夫利nder动态编码的随机信号多参数估计的极限精度，揭示了在高秩相关性和纠缠探测器情况下，平均方差随耗散通道数R呈1/(TR²)的Heisenberg型缩放，适用于集体k体耗散等应用。
Multiparameter quantum metrology at Heisenberg scaling for an arbitrary two-channel linear interferometer with squeezed light
利用 squeezed 光在任意双通道线性干涉仪中实现 Heisenberg 缩放的多参数量子计量，为高精度光学干涉计量提供实验可行的设计原则。
Squeezing currently represents the leading strategy for quantum enhanced precision measurements of a single parameter in a variety of continuous- and discrete-variable settings and technological applications. However, many important physical problems including imaging and field sensing require the simultaneous measurement of multiple unknown parameters. The development of multiparameter quantum metrology is yet hindered by the intrinsic difficulty in finding saturable sensitivity bounds and feasible estimation strategies. Here, we derive the general operational concept of multiparameter squeez…
Quantum metrology aims to exploit quantum phenomena to overcome classical limitations in the estimation of relevant parameters. We consider a probe undergoing a phase shift $φ$ whose generator is randomly sampled according to a distribution with unknown concentration $κ$, which introduces a physical source of noise. We then investigate strategies for the joint estimation of the two parameters $φ$ and $κ$ given a finite number $N$ of interactions with the phase imprinting channel. We consider both single qubit and multipartite entangled probes, and identify regions of the parameters where simul…
Fisher information susceptibility for multiparameter quantum estimation
本文将Fisher信息测量噪声易感性扩展至多参数量子估计场景，以半定规划形式给出数学定义并推导上下界，应用于相位与相位扩散联合估计及光学点源非相干混合参数估计，为多参数测量鲁棒性条件提供明确指示。
In a ubiquitous $SU(2)$ dynamics, achieving the simultaneous optimal estimation of multiple parameters is significant but difficult. Using quantum control to optimize this $SU(2)$ coding unitary evolution is one of solutions. We propose a method, characterized by the nested cross-products of the coefficient vector $\mathbf{X}$ of $SU(2)$ generators and its partial derivative $\partial_\ell \mathbf{X}$, to investigate the control-enhanced quantum multiparameter estimation. Our work reveals that quantum control is not always functional in improving the estimation precision, which depends on the …
We establish the multiparameter quantum Cramér-Rao bound for simultaneously estimating the centroid, the separation, and the relative intensities of two incoherent optical point sources using alinear imaging system. For equally bright sources, the Cramér-Rao bound is independent of the source separation, which confirms that the Rayleigh resolution limit is just an artifact of the conventional direct imaging and can be overcome with an adequate strategy. For the general case of unequally bright sources, the amount of information one can gain about the separation falls to zero, but we show that …
Squeezed-Light-Enhanced Multiparameter Quantum Estimation in Cavity Magnonics
利用退相干光学参量放大器提高腔磁子系统中多参数量子估计的精度，通过抑制量子噪声并分析不同检测方法下的信息量。
Geometric bounds on multiparameter Heisenberg scaling in optical metrology with limited squeezed resources
研究多参量同时估计中，在多模高斯网络里给定压缩探测器时，有多少参数组合能继承海森堡标度。通过分析量子费希尔信息矩阵，得出海森堡标度系数秩的界限，确定饱和条件并构建干涉仪族。
Multiparameter quantum-enhanced adaptive metrology with squeezed light
本文提出一种自适应多参数估计策略，利用实时反馈联合估计相位和压缩水平，在无需先验知识下实现全周期区间低于标准量子极限的精度，建立自校准的量子增强传感框架。
Experimental multiparameter quantum metrology in adaptive regime
本文在可编程集成光子电路中结合量子增强多参数估计与自适应学习，在有限资源下实验演示三个光学相位的同时估计并达到量子极限。
Attaining Fundamental Limits of Multiparameter Incoherent Optical Imaging Using Joint-Detection Quantum Measurements
该研究针对深亚衍射非相干成像问题，推导其量子估计极限，发现可分测量的NH界与Helstrom界存在差距，提出联合探测接收机可渐近达到Helstrom界，且SPADE是近最优可分测量策略。
We show that a significant quantum gain corresponding to squeezed or over-squeezed spin states can be obtained in multiparameter estimation by measuring the Hadamard coefficients of a 1D or 2D signal. The physical platform we consider consists of twolevel atoms in an optical lattice in a squeezed-Mott configuration, or more generally by correlated spins distributed in spatially separated modes. Our protocol requires the possibility to locally flip the spins, but relies on collective measurements. We give examples of applications to scalar or vector field mapping and compressed sensing.
Quantum-limited imaging using diffractive optical neural networks
该研究将成像转化为多参数量子估计，提出基于衍射光学神经网络与光子计数的测量架构，可达到Nagaoka-Hayashi Cramér-Rao界，实现量子极限下的精细图像重建，性能优于直接成像，为相关领域应用开辟可扩展途径。
Multiparameter estimation with two qubit probes in noisy channels
本研究比较了噪声信道下单与双量子比特探针的多参数估计性能，通过计算量子极限发现双探针在多数非恒等信道中更优，但极强噪声下单探针可能超越最大纠缠双探针，并指出实现最终精度需在状态制备与测量阶段均引入纠缠。
Quantum error correction-inspired multiparameter quantum metrology
本文提出一种受量子纠错启发的多参数量子计量学框架，通过引入量子计量学条件并利用有限群的平凡不可约表示来识别最优探针态，从而在无噪声对称多参数估计中使量子 Cramér-Rao 界达到饱和。
Multiparameter sensing of axion dark matter with superconducting-qubit networks
提出利用纠缠超导量子比特网络直接探测QCD轴子暗物质，通过将未知相位作为额外参数构建双参数量子估计框架，结合贝叶斯推断优化网络，在0.1-10微电子伏特质量范围内准确恢复KSVZ和DFSZ耦合，且对退相干和门误差鲁棒。
Controlling multiparameter quantum estimation in exciton-optomechanics system
研究激子-光力学混合系统中同时估计激子-光子耦合强度和激子衰减率的多参数量子估计，发现强耦合和低温可提高精度，外差检测优于零差检测。
Multiparameter quantum sensing and magnetic communications with a hybrid dc and rf optically pumped magnetometer
本文提出一种混合光泵磁力仪（HOPM），利用单一原子自旋系综同时测量直流和射频磁场，实现亚pT灵敏度，并成功演示了背景消除的扩频磁通信，推动了高性能多参数量子传感研究。
Phase estimation is the most investigated protocol in quantum metrology, but its performance is affected by the presence of noise, also in the form of imperfect state preparation. Here we discuss how to address this scenario by using a multiparameter approach, in which noise is associated to a parameter to be measured at the same time as the phase. We present an experiment using two-photon states, and apply our setup to investigating optical activity of fructose solutions. Finally, we illustrate the scaling laws of the attainable precisions with the number of photons in the probe state.
Distributed quantum sensing with measurement-after-interaction strategies
本文研究基于相互作用后测量的多参数量子估计策略，证明其能显著提升灵敏度与抗噪性，并可达到海森堡标度。
Quantum convolutional channels and multiparameter families of 2-unitary matrices
本文提出一种基于卷积的量子通道构造方法，提供更大的非局部参数自由度，并识别了具有最大纠缠能力的卷积通道的条件，同时建立了新的双单位矩阵家族。
Multiparameter quantum estimation with Gaussian states: efficiently evaluating Holevo, RLD and SLD Cramér-Rao bounds
针对无限维高斯量子系统多参数估计中Holevo Cramér-Rao界计算困难的问题，提出基于半定规划的高效数值方法，可统一计算HCRB、SLD和RLD界，并通过相位损耗、压缩位移两个场景验证了适用性。
Squeezed light and coherent feedback enhanced multiparameter quantum estimation in a double-cavity optomechanics: steady and dynamical states
本研究在耦合腔光力学平台中，结合参量放大与相干光反馈，实现了光力学耦合强度和腔耗散率的多参数量子估计，明确了两类调控机制对估计精度的影响及最优参数区域。
Deterministic and programmable generation of mechanical multipartite entangled states
本研究利用与超导transmon量子比特耦合的高次谐波体声波谐振器，通过最优控制等距映射确定性可编程生成W、GHZ等多体机械纠缠态，实现关联噪声传感，为机械系统多体纠缠制备提供可扩展方法。
Multiparameter estimation is a general problem that aims at measuring unknown physical quantities, obtaining high precision in the process. In this context, the adoption of quantum resources promises a substantial boost in the achievable performances with respect to the classical case. However, several open problems remain to be addressed in the multiparameter scenario. A crucial requirement is the identification of suitable platforms to develop and experimentally test novel efficient methodologies that can be employed in this general framework. We report the experimental implementation of a r…
The problem of estimating multiple loss parameters of an optical system using the most general ancilla-assisted parallel strategy is solved under energy constraints. An upper bound on the quantum Fisher information matrix is derived assuming that the environment modes involved in the loss interaction can be accessed. Any pure-state probe that is number-diagonal in the modes interacting with the loss elements is shown to exactly achieve this upper bound even if the environment modes are inaccessible, as is usually the case in practice. We explain this surprising phenomenon, and show that measur…
Quantum noise scaling in continuously operating multiparameter sensors
该研究通过实验揭示连续多参数传感器中量子噪声标度特性及资源受限的权衡，确立了其最佳运行的量子极限。
In this paper, we propose a novel scheme that can generate two-atom maximally entangled states from pure product states and mixed states using linear optics. Because the scheme can generate pure maximally entangled states from mixed states, we denote it as purification-like generation scheme.
We present a scheme to produce an entangled four-photon state from two pairs of entangled two-photon states. Such entangled four-photon states are equivalent to the quantum state of two maximally entangled spin-1 particles. The scheme can also be generated to prepare an entangled 2N-photon state from N pairs of entangled two-photon states. Such multi-photon states play a crucial role in fundamental tests of quantum mechanics versus local realism and in many quantum information and quantum computation schemes.
In this paper, we describe how to realize conditional frequency entanglement swapping and to produce probabilisticly a three-photon frequency entangled state from two pairs of frequency entangled states by using an Acoustic-Optical-Modulator. Both schemes are very simple and may be implementable in practice.
Advances in multiparameter quantum sensing and metrology
本文综述多参数量子传感与计量学，涵盖基本框架、极限灵敏度界、最优测量策略及量子不相容性，并讨论分布式传感实验与优化技术，旨在连接理论与实验，推动下一代量子传感器发展。
In the recent years important experimental advances in resonant electro-optic modulators as high efficient sources for coherent frequency combs and as devices for quantum information transfer have been realized, where strong optical and microwave mode coupling were achieved. These features suggest electro-optic based devices as candidates for entangled optical frequency comb sources. In the present I study the generation of entangled optical frequency combs in mm-sized resonant electro-optic modulators. These devices profit from the experimentally proven advantages such as nearly constant opti…
We describe several different methods for generating the entangled ancilla states that are required for linear optics quantum computing. We show that post-selection can be used in combination with linear optical elements to generate the entangled ancilla, but with an exponentially-small efficiency. Alternatively, the ancilla can be efficiently generated using solid-state devices consisting of quantum wells coupled with tunnel junctions. Finally, we consider the possibility of using encoded ancilla in order to reduce the effects of decoherence and measurement errors.
To acquire the best path-entangled photon Fock states for robust quantum optical metrology with parity detection, we calculate phase information from a lossy interferometer by using twin entangled Fock states. We show that (a) when loss is less than 50% twin entangled Fock states with large photon number difference give higher visibility while when loss is higher than 50% the ones with less photon number difference give higher visibility; (b) twin entangled Fock states with large photon number difference give sub-shot-noise limit sensitivity for phase detection in a lossy environment. This res…
We present an optical design where polarization-entangled photon pairs are generated within two $β$-Barium Borate crystals whose optical axes are parallel. This design increases the spatial mode overlap of the emitted photon pairs enhancing single mode collection without the need for additional spatial walk-off compensators. The observed photon pair rate is at least 65000 pairs/s/mW with a quantum state fidelity of 99.53$\pm$0.22% when pumped with an elliptical spatial profile.
We propose a universal scheme for the probabilistic generation of an arbitrary multimode entangled state of light with finite expansion in Fock basis. The suggested setup involves passive linear optics, single photon sources, strong coherent laser beams, and photodetectors with single-photon resolution. The efficiency of this setup may be greatly enhanced if, in addition, a quantum memory is available.
Entangled photons are pivotal elements in emerging quantum information technologies. While several schemes are available for the production of entangled photons, they typically require the assistance of cumbersome optical elements to couple them to other components involved in logic operations. Here, we introduce a scheme by which entangled photon pairs are directly generated as guided mode states in optical waveguides. The scheme relies on the intrinsic nonlinearity of the waveguide material, circumventing the use of bulky optical components. Specifically, we consider an optical fiber under n…
We propose two types of quantum dense coding communication networks with optical continuous variables, in which a quadripartite entangled state of the optical field with totally three-party correlations of quadrature amplitudes is utilized. In the networks, the exchange of information between any two participants can be manipulated by one or two of the remaining participants. The channel capacities for a variety of communication protocols are numerically calculated. Due to the fact that the quadripartite entangled states applied in the communication systems have been successfully prepared alre…
A quantum communication network can be constructed by distributing a multipartite entangled state to space-separated nodes. Entangled optical beams with highest flying speed and measurable brightness can be used as carriers to convey information in quantum communication networks. Losses and noises existing in real communication channels will reduce or even totally destroy entanglement. The phenomenon of disentanglement will result in the complete failure of quantum communication. Here, we present the experimental demonstrations on the disentanglement and the entanglement revival of tripartite …
The concatenated Greenberger-Horne-Zeilinger (C-GHZ) state is a new type of multipartite entangled state, which has potential application in future quantum information. In this paper, we propose a protocol of constructing arbitrary C-GHZ entangled state approximatively. Different from the previous protocols, each logic is encoded in the coherent state. This protocol is based on the linear optics, which is feasible in experimental technology. This protocol may be useful in quantum information based on the C-GHZ state.
The concept of directionally unbiased optical multiports is introduced, in which photons may reflect back out the input direction. A linear-optical implementation is described, and the simplest three-port version studied. Symmetry arguments demonstrate potential for unusual quantum information processing applications. The devices impose group structures on two-photon entangled Bell states and act as universal Bell-state processors to implement probabilistic quantum gates acting on state symmetries. These multiports allow optical scattering experiments to be carried out on arbitrary undirected …
We proposed two linear optics based entanglement concentration protocols (ECPs) to obtain maximally entangled 4-mode Cluster-type entangled coherent state (ECS) from less (partially) entangled Cluster-type ECS. The first ECP is designed using a superposition of single-mode coherent state with two unknown parameters, whereas the second ECP is obtained using a superposition of single-mode coherent state and a superposition of two-mode coherent state with four unknown parameters. The success probabilities have been calculated for both the ECPs. Necessary quantum circuits enabling future experimen…
Robust Quantum Sensing with Multiparameter Decorrelation
该研究提出一种结合多参数估计理论与机器学习的鲁棒量子传感协议设计方法，可实现目标信号与干扰参数去相关，并在可重构光晶格加速度计上验证了效果，为量子计量与计算应用提供新思路。
We proposed two entanglement concentration protocols (ECPs) to obtain maximally entangled Greenberger-Horne-Zeilinger (GHZ)-type entangled coherent state (ECS) from the corresponding partially entangled GHZ-type ECSs. We obtained the first ECP using a partially entangled GHZ-type ECS assisted with a superposition of single-mode coherent state, however the second ECP is designed using two copies of partially entangled GHZ-type ECSs. The success probabilities have also been calculated and discussed for both the ECPs. We have further compared the success probabilities of our first ECP for 3-mode …
We propose a feasible scheme to create $n$-party ($n\geq 2$) polarization-entangled photon states in a controllable way. The scheme requires only single-photon sources, single-photon quantum non-demolition measurement (SP-QNDM) and simple linear optical elements, usually with high perfections. The SP-QNDM acts as a non-destructive projection measurement onto the wanted entangled states and filters out the unwanted terms. Our scheme in fact realizes entanglement of non-interacting photons; the interaction occurs only implicitly in the optical elements and SP-QNDM. We also briefly consider purif…
We review and compare Bell-state measurement and quantum teleportation schemes using linear optics with three different types of resources, i.e., two-photon pairs, entangled coherent states and hybrid entangled states. Remarkably, perfect teleportation with linear optics is possible in principle based on a hybrid approach that combines two-photon pairs and entangled coherent states. It turns out that hybrid approach allows to perform Bell-state measurement and local Pauli operations in a deterministic way, while it requires photon number resolving measurements.
Reconfigurable distribution of entangled states is essential for operation of quantum networks connecting multiple devices such as quantum memories and quantum computers. We introduce new quantum distribution network architecture enabling control of the entangled state propagation direction using linear-optical devices and phase shifters and offering reconfigurable connections between multiple quantum nodes. The basic two-photon entanglement distribution scheme is first introduced to illustrate the principle of operation. The scheme is then extended to a network structure with increased number…
We address binary optical communication in single-mode and entangled quantum noisy channels. For single-mode we present a systematic comparison between direct photodetection and homodyne detection in realistic conditions, i.e. taking into account the noise that occurs both during the propagation and the detection of the signals. We then consider entangled channels based on twin-beam state of radiation, and show that with realistic heterodyne detection the error probability at fixed channel energy is reduced in comparison to the single-mode cases for a large range of values of quantum efficienc…
The positivity of the partial transpose is in general only a necessary condition for separability. There exist quantum states that are not separable, but nevertheless are positive under partial transpose. States of this type are known as bound entangled states meaning that these states are entangled but they do not allow distillation of pure entanglement by means of local operations and classical communication (LOCC). We present a parametrization of a class of $2\times 2$ bound entangled Gaussian states for bipartite continuous-variable quantum systems with two modes on each side. We propose a…
The quantum characteristics of sum-frequency process in an optical cavity with an input signal optical beam, which is a half of entangled optical beams, are analyzed. The calculated results show that the quantum properties of the signal beam can be maintained after its frequency is conversed during the intracavity nonlinear optical interaction. The frequency-conversed output signal beam is still in an entangled state with the retained other half of initial entangled beams. The resultant quantum correlation spectra and the parametric dependences of the correlations on the initial squeezing fact…
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