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arXiv:1004.2361 · Physical Review Letters

Enhanced Resolution of Lossy Interferometry by Coherent Amplification of Single Photons

Chiara Vitelli, Nicolò Spagnolo, Lorenzo Toffoli, Fabio Sciarrino, F. De Martini

Published Sep 8, 2010• 30 citations
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Abstract

In the quantum sensing context most of the efforts to design novel quantum techniques of sensing have been constrained to idealized, noise-free scenarios, in which effects of environmental disturbances could be neglected. In this work, we propose to exploit optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive scenario. By performing the amplification process on the microscopic probe after the interaction with the sample, we can beat the losses' detrimental effect on the phase measurement which affects the single-photon state after its interaction with the sample, and thus improve the achievable sensitivity.

DOI
10.1103/physrevlett.105.113602

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In the quantum sensing context most of the efforts to design novel quantum techniques of sensing have been constrained to idealized, noise-free scenarios, in which effects of environmental disturbances could be neglected. In this work, we propose to exploit optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive scenario. By performing the amplification process on the microscopic probe after the interaction with the sample, we can beat the losses' detrimental effect on the phase measurement which affects the single-photon state after its interaction with the sample, and thus improve the achievable sensitivity.
In the optical sensing context one of the main challenge is to design and implement novel techniques of sensing optimized to work in a lossy scenario, in which effects of environmental disturbances can destroy the benefits deriving from the adoption of quantum resources. Here we describe the experimental implementation of a protocol based on the process of optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive scenario. By performing the amplification process on a microscopic probe after the interaction with the sample, we can beat the losses detrimental effect on the phase measurement which affects the single photon state after its interaction with the sample, and thus improve the achievable sensitivity.
The aim of quantum sensing is to develop quantum methods to extract the maximum amount of information from a system with minimal disturbance upon it. Indeed, the possibility of performing precision measurements by adopting quantum resources can increase the achievable precision going beyond the semiclassical regime of operation. However the quantum states suitable for quantum metrology protocols, result extremely fragile under losses and decoherence, unavoidable in experimental implementations, destroying completely quantum benefits. This scenario puts the beating of realistic, noisy environments as the main challenge in developing quantum sensing.
The sensitivity in optical interferometry is strongly affected by losses during the signal propagation or at the detection stage. The optimal quantum states of the probing signals in the presence of loss were recently found. However, in many cases of practical interest, their associated accuracy is worse than the one obtainable without employing quantum resources (e.g., entanglement and squeezing) but neglecting the detector's loss. Here, we detail an experiment that can reach the latter even in the presence of imperfect detectors: it employs a phase-sensitive amplification of the signals after the phase sensing, before the detection. We experimentally demonstrated the feasibility of a phase estimation experiment able to reach its optimal working regime. Since our method uses coherent states as input signals, it is a practical technique that can be used for high-sensitivity interferometry and, in contrast to the optimal strategies, does not require one to have an exact characterization of the loss beforehand.
Optical interferometers, as precision measurement tools, inevitably experience optical path losses in practical applications, which introduce unavoidable vacuum noise and reduce the sensitivity in the phase estimation. To mitigate the effects of losses on sensitivity, we propose an enhanced interferometer scheme that integrates a Raman amplifier. This amplifier is strategically positioned within the lossy interference arm to counteract the reduction in phase sensitivity caused by losses. Our research highlights the crucial role of amplifier positioning, revealing that pre-amplification (PRA, placing the amplifier before the lossy section) significantly outperforms post-amplification (POA, placing the amplifier after the lossy section). PRA effectively enhances sensitivity by increasing the number of phase-sensitive particles and minimizing noise amplification. As the loss increases, the superiority of PRA in mitigating loss effects becomes increasingly evident. To validate our approach, we conducted experimental demonstrations. When the losses reach 90%, PRA experimentally achieves a sensitivity improvement of 4.6 dB compared with the case of only loss without the amplifier, equivalent to increasing the input laser power by over 8 times. PRA can effectively improve the robustness against losses for the practical application solely through the use of a coherent amplifier, with a simple technical implementation yet remarkable enhancement effects. We believe that current PRA-enhanced interferometry facilitates the practical implementation of phase measurement in environments characterized by significant loss.