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- 摘要
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Modular-value-based metrology with spin coherent pointers
摘要： We discuss an optimal modular-value-based measurement with a spin coherent pointer: A quantum system is exposed to a field whose strength is to be estimated through its modular value. We evaluate the quantum Fisher information as a figure of merit. We found that the modular-value-based measurement can reach the same ultimate precision limit of the estimation as those of measurements without postselections. The quantum Fisher information can be increased when the dimension of the pointer state increases. We also consider the pointer under a phase-flip error. Our study should motivate researchers to apply the modular-value-based measurements for quantum metrology.
关键词： Quantum Fisher information,Modular values,Weak values,Quantum metrology
更新于2025-09-23 15:21:21
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Experimental optical phase measurement approaching the exact Heisenberg limit
摘要： The use of quantum resources can provide measurement precision beyond the shot-noise limit (SNL). The task of ab initio optical phase measurement—the estimation of a completely unknown phase—has been experimentally demonstrated with precision beyond the SNL, and even scaling like the ultimate bound, the Heisenberg limit (HL), but with an overhead factor. However, existing approaches have not been able—even in principle—to achieve the best possible precision, saturating the HL exactly. Here we demonstrate a scheme to achieve true HL phase measurement, using a combination of three techniques: entanglement, multiple samplings of the phase shift, and adaptive measurement. Our experimental demonstration of the scheme uses two photonic qubits, one double passed, so that, for a successful coincidence detection, the number of photon-passes is N = 3. We achieve a precision that is within 4% of the HL. This scheme can be extended to higher N and other physical systems.
关键词： Heisenberg limit,adaptive measurement,entanglement,quantum metrology,optical phase measurement
更新于2025-09-23 15:21:01
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Entangled States of Atomic Solitons for Quantum Metrology
摘要： The formation of multiparticle maximally path-entangled states (known as N00N-states) are considered along with their use in quantum metrology. It is shown how the standard quantum limit can be overcome and the Heisenberg limit can be reached when measuring the linear phase shift. It is also shown how the Heisenberg limit can be overcome when measuring the parameters of a medium in nonlinear quantum metrology.
关键词： quantum metrology,Heisenberg limit,Bose–Einstein condensates,standard quantum limit,N00N-states
更新于2025-09-23 15:19:57
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Demonstration of a Reconfigurable Entangled Radio-Frequency Photonic Sensor Network
摘要： Quantum metrology takes advantage of nonclassical resources such as entanglement to achieve a sensitivity level below the standard quantum limit. To date, almost all quantum-metrology demonstrations are restricted to improving the measurement performance at a single sensor, but a plethora of applications require multiple sensors that work jointly to tackle distributed sensing problems. Here, we propose and experimentally demonstrate a reconfigurable sensor network empowered by continuous-variable (CV) multipartite entanglement. Our experiment establishes a connection between the entanglement structure and the achievable quantum advantage in different distributed sensing problems. The demonstrated entangled sensor network is composed of three sensor nodes each equipped with an electro-optic transducer for the detection of radio-frequency (RF) signals. By properly tailoring the CV multipartite entangled states, the entangled sensor network can be reconfigured to maximize the quantum advantage in distributed RF sensing problems such as measuring the angle of arrival of an RF field. The rich physics of CV multipartite entanglement unveiled by our work would open a new avenue for distributed quantum sensing and would lead to applications in ultrasensitive positioning, navigation, and timing.
关键词： distributed sensing,entanglement,quantum metrology,electro-optic transducer,radio-frequency
更新于2025-09-23 15:19:57
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Optimal Gaussian measurements for phase estimation in single-mode Gaussian metrology
摘要： The central issue in quantum parameter estimation is to find out the optimal measurement setup that leads to the ultimate lower bound of an estimation error. We address here a question of whether a Gaussian measurement scheme can achieve the ultimate bound for phase estimation in single-mode Gaussian metrology that exploits single-mode Gaussian probe states in a Gaussian environment. We identify three types of optimal Gaussian measurement setups yielding the maximal Fisher information depending on displacement, squeezing, and thermalization of the probe state. We show that the homodyne measurement attains the ultimate bound for both displaced thermal probe states and squeezed vacuum probe states, whereas for the other single-mode Gaussian probe states, the optimized Gaussian measurement cannot be the optimal setup, although they are sometimes nearly optimal. We then demonstrate that the measurement on the basis of the product quadrature operators ^X^P + ^P^X, i.e., a non-Gaussian measurement, is required to be fully optimal.
关键词： Gaussian states,Fisher information,optimal measurements,quantum metrology,phase estimation
更新于2025-09-19 17:15:36
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Phononic-waveguide-assisted steady-state entanglement of silicon-vacancy centers
摘要： Multiparticle entanglement is of great significance for quantum metrology and quantum information processing. We present here an efficient scheme for generating stable multiparticle entanglement in a solid-state setup, where an array of silicon-vacancy centers are embedded in a quasi-one-dimensional acoustic diamond waveguide. In this scheme, the continuum of phonon modes induces a controllable dissipative coupling among the SiV centers. We show that, by an appropriate choice of the distance between the SiV centers, the dipole-dipole interactions can be switched off due to destructive interference, thus realizing a Dicke superradiance model. This gives rise to an entangled steady state of SiV centers with high fidelities. The protocol provides a feasible setup for the generation of multiparticle entanglement in a solid-state system.
关键词： Multiparticle entanglement,quantum information processing,acoustic diamond waveguide,quantum metrology,silicon-vacancy centers,Dicke superradiance model
更新于2025-09-19 17:13:59
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Spatial squeezing in bright twin beams generated with four-wave mixing: Constraints on characterization with an electron-multiplying charge-coupled-device camera
摘要： The observation of spatial quantum noise reduction, or spatial squeezing, with a large number of photons can lead to a significant advantage in quantum imaging and quantum metrology due to the scaling of the signal-to-noise ratio with the number of photons. Here we present a systematic study of the limiting factors that play a role on the measurement of spatial squeezing with an electron-multiplying charge-coupled device (EMCCD) camera in the limit of bright quantum states of light generated with a four-wave mixing process in an atomic vapor cell. We detect a total number of photons per beam of the order 108 in 1 μs pulses, which corresponds to a photon flux per beam of the order of 1014 photons per second. We then investigate the role of different parameters, such as cell temperature, pump power, laser detunings, scattered pump background noise, and timing sequences for the image acquisition with the EMCCD camera, on the level of spatial squeezing. We identify critical parameters to obtain an optimum squeezing level and demonstrate that for bright beams it is essential to acquire images at a rate fast enough to overcome the effect of classical technical noise.
关键词： spatial squeezing,atomic vapor cell,quantum imaging,spatial quantum noise reduction,quantum metrology,four-wave mixing,EMCCD camera
更新于2025-09-12 10:27:22
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Quantum-enhanced sensing using non-classical spin states of a highly magnetic atom
摘要： Coherent superposition states of a mesoscopic quantum object play a major role in our understanding of the quantum to classical boundary, as well as in quantum-enhanced metrology and computing. However, their practical realization and manipulation remains challenging, requiring a high degree of control of the system and its coupling to the environment. Here, we use dysprosium atoms—the most magnetic element in its ground state—to realize coherent superpositions between electronic spin states of opposite orientation, with a mesoscopic spin size J = 8. We drive coherent spin states to quantum superpositions using non-linear light-spin interactions, observing a series of collapses and revivals of quantum coherence. These states feature highly non-classical behavior, with a sensitivity to magnetic fields enhanced by a factor 13.9(1.1) compared to coherent spin states—close to the Heisenberg limit 2J = 16—and an intrinsic fragility to environmental noise.
关键词： Heisenberg limit,Dysprosium atoms,Quantum-enhanced sensing,Non-classical spin states,Quantum metrology
更新于2025-09-10 09:29:36
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Quantum-Limited Loss Sensing: Multiparameter Estimation and Bures Distance between Loss Channels
摘要： 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 measuring the Schmidt bases of the probe is a parameter-independent optimal measurement. Our results imply that multiple copies of two-mode squeezed vacuum probes with an arbitrarily small nonzero degree of squeezing, or probes prepared using single-photon states and linear optics, can achieve quantum-optimal performance in conjunction with on-off detection. We also calculate explicitly the energy-constrained Bures distance between any two product loss channels. Our results are relevant to standoff image sensing, biological imaging, absorption spectroscopy, and photodetector calibration.
关键词： Bures distance,loss sensing,quantum Fisher information,optical systems,Quantum metrology
更新于2025-09-09 09:28:46
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Resolving unattainable Cramer-Rao bounds for quantum sensors
摘要： In quantum metrology, it is widely believed that the quantum Cram′er-Rao bound is an attainable bound. However, this is not always true. In order to clarify this point, we explain why the quantum Cram′er-Rao bound cannot be attained. Here, we investigate noiseless channel estimation under energy constraint for states, using a physically reasonable error function, and present a state achieving the optimal rate as well as the attainable bound. We propose an experimental generation of the optimal states for enhanced metrology using squeezing transformations. This makes phase/unitary estimation physically implementable.
关键词： quantum sensor,quantum metrology,phase estimation
更新于2025-09-09 09:28:46