scholarly journals Channel Simulation in Quantum Metrology

2018 ◽  
Vol 5 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Riccardo Laurenza ◽  
Cosmo Lupo ◽  
Gaetana Spedalieri ◽  
Samuel L. Braunstein ◽  
Stefano Pirandola
Keyword(s):  
Parameter Estimation ◽  
Adaptive Estimation ◽  
Continuous Variable ◽  
Upper And Lower Bounds ◽  
Quantum Limit ◽  
Standard Quantum Limit ◽  
Adaptive Protocols ◽  
Channel Simulation ◽  
Primitive Operation ◽  
Cramer Rao Bound

Abstract In this review we discuss how channel simulation can be used to simplify the most general protocols of quantum parameter estimation, where unlimited entanglement and adaptive joint operations may be employed. Whenever the unknown parameter encoded in a quantum channel is completely transferred in an environmental program state simulating the channel, the optimal adaptive estimation cannot beat the standard quantum limit. In this setting, we elucidate the crucial role of quantum teleportation as a primitive operation which allows one to completely reduce adaptive protocols over suitable teleportation-covariant channels and derive matching upper and lower bounds for parameter estimation. For these channels,wemay express the quantum Cramér Rao bound directly in terms of their Choi matrices. Our review considers both discrete- and continuous-variable systems, also presenting some new results for bosonic Gaussian channels using an alternative sub-optimal simulation. It is an open problem to design simulations for quantum channels that achieve the Heisenberg limit.

scholarly journals Fake calibration attack using a beam sampler in a continuous variable-quantum key distribution system

2020 ◽  
Vol 66 (2 Mar-Apr) ◽  
pp. 228
Author(s):  
J. A. Lopez-Leyva ◽  
A. Talamantes-Alvarez ◽  
E. A. Mejia ◽  
J. Estrada ◽  
M. Ponce Camacho ◽  
...  
Keyword(s):  
Bit Error Rate ◽  
Error Rate ◽  
Distribution System ◽  
Continuous Variable ◽  
Quantum Limit ◽  
Standard Quantum ◽  
Standard Quantum Limit ◽  
Quantum Bit ◽  
Quantum Bit Error Rate ◽  
Calibration Attack

A Fake Calibration Attack process for a Continuous Variable-Quantum Key Distribution system using a Beam Sampler is presented. The Fake Calibration Attack allows a calibration that balances the Standard Quantum Limit for all the optical path in the experiment (differential Standard Quantum Limit is ≈ 0.39 dB) allowing Eve to acquire ≈ 0.0671 for a particular information quadrature which establishes a Quantum Bit Error Rate ≈ 5.8%. As a final result, the balancing of the Standard Quantum Limit for both states of polarization signals allows maintaining the overall Quantum Bit Error Rate at a particular value ≈ 3%, which implies an important basis for detecting a potential spy considering the minimum Quantum Bit Error Rate.

scholarly journals A variational toolbox for quantum multi-parameter estimation

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Johannes Jakob Meyer ◽  
Johannes Borregaard ◽  
Jens Eisert
Keyword(s):  
Parameter Estimation ◽  
Information Science ◽  
Quantum Algorithms ◽  
Continuous Variable ◽  
General Interest ◽  
Quantum Metrology ◽  
Estimation Problems ◽  
General Parameter ◽  
Quantum Technology ◽  
Aided Design

AbstractWith an ever-expanding ecosystem of noisy and intermediate-scale quantum devices, exploring their possible applications is a rapidly growing field of quantum information science. In this work, we demonstrate that variational quantum algorithms feasible on such devices address a challenge central to the field of quantum metrology: The identification of near-optimal probes and measurement operators for noisy multi-parameter estimation problems. We first introduce a general framework that allows for sequential updates of variational parameters to improve probe states and measurements and is widely applicable to both discrete and continuous-variable settings. We then demonstrate the practical functioning of the approach through numerical simulations, showcasing how tailored probes and measurements improve over standard methods in the noisy regime. Along the way, we prove the validity of a general parameter-shift rule for noisy evolutions, expected to be of general interest in variational quantum algorithms. In our approach, we advocate the mindset of quantum-aided design, exploiting quantum technology to learn close to optimal, experimentally feasible quantum metrology protocols.

scholarly journals Quantum metrology with full and fast quantum control

Quantum ◽  
2017 ◽  
Vol 1 ◽  
pp. 27 ◽  
Author(s):  
Pavel Sekatski ◽  
Michalis Skotiniotis ◽  
Janek Kołodyński ◽  
Wolfgang Dür
Keyword(s):  
Quantum Control ◽  
Frequency Estimation ◽  
Fixed Number ◽  
Constant Factor ◽  
Quantum Limit ◽  
Single Shot ◽  
Standard Quantum Limit ◽  
Parallel Scheme ◽  
Rank One ◽  
Fast Control

We establish general limits on how precise a parameter, e.g. frequency or the strength of a magnetic field, can be estimated with the aid of full and fast quantum control. We consider uncorrelated noisy evolutions of N qubits and show that fast control allows to fully restore the Heisenberg scaling (~1/N^2) for all rank-one Pauli noise except dephasing. For all other types of noise the asymptotic quantum enhancement is unavoidably limited to a constant-factor improvement over the standard quantum limit (~1/N) even when allowing for the full power of fast control. The latter holds both in the single-shot and infinitely-many repetitions scenarios. However, even in this case allowing for fast quantum control helps to increase the improvement factor. Furthermore, for frequency estimation with finite resource we show how a parallel scheme utilizing any fixed number of entangled qubits but no fast quantum control can be outperformed by a simple, easily implementable, sequential scheme which only requires entanglement between one sensing and one auxiliary qubit.

scholarly journals Entanglement-enhanced matter-wave interferometry in a high-finesse cavity

2021 ◽  
Author(s):  
James Thompson ◽  
Graham Greve ◽  
Chengyi Luo ◽  
Baochen Wu
Keyword(s):  
Cavity Qed ◽  
Degrees Of Freedom ◽  
Inertial Sensors ◽  
Mean Field ◽  
New Physics ◽  
Matter Wave ◽  
Quantum Limit ◽  
Entangled State ◽  
Standard Quantum ◽  
Standard Quantum Limit

Abstract Entanglement is a fundamental resource that allows quantum sensors to surpass the standard quantum limit set by the quantum collapse of independent atoms. Collective cavity-QED systems have succeeded in generating large amounts of directly observed entanglement involving the internal degrees of freedom of laser-cooled atomic ensembles. Here we demonstrate cavity-QED entanglement of external degrees of freedom to realize a matter-wave interferometer of 700 atoms in which each individual atom falls freely under gravity and simultaneously traverses two paths through space while also entangled with the other atoms. We demonstrate both quantum non-demolition measurements and cavity-mediated spin interactions for generating squeezed momentum states with directly observed metrological gain 3.4^{+1.1}_{-0.9} dB and 2.5^{+0.6}_{-0.6} dB below the standard quantum limit respectively. An entangled state is for the first time successfully injected into a Mach-Zehnder light-pulse interferometer with 1.7^{+0.5}_{-0.5} dB of directly observed metrological enhancement. These results open a new path for combining particle delocalization and entanglement for inertial sensors, searches for new physics, particles, and fields, future advanced gravitational wave detectors, and accessing beyond mean-field quantum many-body physics.

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