QUANTUM INTERFEROMETRY AT ZERO AND FINITE TEMPERATURE WITH TWO-MODE BOSONIC JOSEPHSON JUNCTIONS

We analyze phase interferometry realized with a bosonic Josephson junction (BJJ) made of trapped dilute and ultracold atoms. By using a suitable phase sensitivity indicator we study the zero temperature junction-states useful to achieve sub shot-noise precisions. Sub shot-noise phase shift sensitivities can be reached even at finite temperature under a suitable choice of the junction state. We infer a scaling law in terms of the size system (that is, the number of particles) for the temperature at which the shot-noise limit is not overcome anymore.

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Quantum Fisher information for superpositions of spin states

Quantum Information and Computation ◽

10.26421/qic10.5-6-8 ◽

2010 ◽

Vol 10 (5&6) ◽

pp. 498-508

Author(s):

H.-N. Xiong ◽

J. Ma ◽

W.-F. Liu ◽

X. Wang

Keyword(s):

Fisher Information ◽

Shot Noise ◽

Quantum Fisher Information ◽

Entanglement Measure ◽

Spin States ◽

Phase Sensitivity ◽

Noise Limit ◽

Necessary And Sufficient ◽

Shot Noise Limit ◽

Dicke States

In terms of quantum Fisher information, a quantity $\chi^{2}$ was introduced by Pezz\'{e} and Smerzi, which is a multiparticle entanglement measure, and provides a necessary and sufficient condition for sub-shot-noise phase estimation sensitivity. We derive a general expression of $\chi ^{2}$ for arbitrary symmetric multiqubit states with nonzero mean spins. It is shown that the entangled symmetric states are useful for phase sensitivity beyond the shot-noise limit. Using the expression, we explicitly examine a series of superpositions of spin states. We find that the superpositions of Dicke states perform better than Dicke states themselves in phase esitmation. Although the spin coherent states themselves only have a shot-noise limit phase sensitivity, their superpositions may reach the Heisenberg limit.

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Surpassing the shot-noise limit by homodyne-mediated feedback

Optics Letters ◽

10.1364/ol.41.003932 ◽

2016 ◽

Vol 41 (17) ◽

pp. 3932 ◽

Cited By ~ 4

Author(s):

Guofeng Zhang ◽

Hanjie Zhu

Keyword(s):

Shot Noise ◽

Noise Limit ◽

Shot Noise Limit

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Overcoming detection loss and noise in squeezing-based optical sensing

npj Quantum Information ◽

10.1038/s41534-021-00407-0 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Gaetano Frascella ◽

Sascha Agne ◽

Farid Ya. Khalili ◽

Maria V. Chekhova

Keyword(s):

Shot Noise ◽

Optical Sensing ◽

Detection Efficiency ◽

Signal To Noise Ratio ◽

Real Life ◽

Squeezed States ◽

Squeezed Light ◽

Noise Limit ◽

Imaging And Spectroscopy ◽

Shot Noise Limit

AbstractAmong the known resources of quantum metrology, one of the most practical and efficient is squeezing. Squeezed states of atoms and light improve the sensing of the phase, magnetic field, polarization, mechanical displacement. They promise to considerably increase signal-to-noise ratio in imaging and spectroscopy, and are already used in real-life gravitational-wave detectors. But despite being more robust than other states, they are still very fragile, which narrows the scope of their application. In particular, squeezed states are useless in measurements where the detection is inefficient or the noise is high. Here, we experimentally demonstrate a remedy against loss and noise: strong noiseless amplification before detection. This way, we achieve loss-tolerant operation of an interferometer fed with squeezed and coherent light. With only 50% detection efficiency and with noise exceeding the level of squeezed light more than 50 times, we overcome the shot-noise limit by 6 dB. Sub-shot-noise phase sensitivity survives up to 87% loss. Application of this technique to other types of optical sensing and imaging promises a full use of quantum resources in these fields.

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Optimization of Detectability in Laser-Based Polarimeters

Applied Spectroscopy ◽

10.1366/0003702894204425 ◽

1989 ◽

Vol 43 (8) ◽

pp. 1337-1341 ◽

Cited By ~ 6

Author(s):

Xiaobing Xi ◽

Edward S. Yeung

Keyword(s):

Shot Noise ◽

Experimental Verification ◽

High Frequency ◽

Ohmic Heating ◽

Unit Length ◽

Power Input ◽

Upper Limit ◽

High Modulation ◽

Noise Limit ◽

Shot Noise Limit

To optimize the performance of a laser-based polarimeter, a mathematical simulation was performed. High-modulation currents allow a corresponding increase in signal. However, the effect of ohmic heating puts an upper limit on the power input to the solenoid. With this constraint, one can systematically choose the wire diameter and the number of turns per unit length. An experimental verification of the optimized parameters provided performance approaching the shot-noise limit. By using higher modulation currents, one can operate at 1 kHz to achieve detectability in the microdegree range, without the complications of high-frequency (100 kHz) modulation.

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