Entanglement-Enhanced Sensing in a Lossy and Noisy Environment

Abstract

Nonclassical states are essential for optics-based quantum information processing, but their fragility limits their utility for practical scenarios in which loss and noise inevitably degrade, if not destroy, nonclassicality. Exploiting nonclassical states in quantum metrology yields sensitivity advantages over all classical schemes delivering the same energy per measurement interval to the sample being probed. These enhancements, almost without exception, are severely diminished by quantum decoherence. Here, we experimentally demonstrate an entanglement-enhanced sensing system that is resilient to quantum decoherence. We employ entanglement to realize a 20% signal-to-noise ratio improvement over the optimum classical scheme in an entanglement-breaking environment plagued by 14 dB of loss and a noise background 75 dB stronger than the returned probe light. Our result suggests that advantageous quantumsensing technology could be developed for practical situations. DOI: 10.1103/PhysRevLett.114.110506 PACS numbers: 03.67.-a, 03.65.Ta, 42.50.Dv Quantum information processing (QIP) exploits fundamental quantum-mechanical properties to realize capabilities beyond the reach of classical physics. Nonclassical states are essential for optics-based QIP, providing the bases for quantum teleportation [1-3], device-independent quantum key distribution [4], quantum computing [5,6], and quantum metrology [7]. Nonclassical states can increase the signal-to-noise ratios (SNRs) of quantummetrology systems. Indeed, squeezed states have been employed to beat the classical-state limits in optical-phase tracking [8,9], biological sensing [10], and gravitational wave detection [11,12]. Squeezed states, however, are vulnerable to loss: a 10 dB SNR enhancement without loss degrades to 1 dB in a system with 6 dB of loss. Under ideal conditions, N00N states, which are superposition states of N photons in one mode and vacuum in another mode, and vice versa, yield SNR improvements comparable to those of squeezed states [13][14][15][16], but noise injection can easily render N00N states impotent in this regard [17,18]. Consequently, quantum decoherence, arising from environmental loss and noise, largely prevents any quantum-sensing performance advantage, casting doubt on the utility of QIP systems for practical situations.Quantum illumination (QI) is a radically different paradigm that utilizes nonclassical states to achieve an appreciable performance enhancement in the presence of quantum decoherence. QI can defeat eavesdropping on a communication link [19][20][21][22], and boost the SNR of a sensing system [23][24][25][26][27][28][29]. QI systems are comprised of (1) a source that emits entangled signal and idler beams; (2) an interaction in which the signal beam (used as a probe) is subjected to environmental loss, modulation, and noise en route from the source to the receiver; and (3) a receiver that makes a joint measurement on the returned signal beam and the idler beam, which has been stored in a quantum memory, to extract informat...

Cryptographic Aspects of Quantum Reading

“…This approach is known as quantum reading [11] (see also follow-up papers [12][13][14][15][16][17][18][19][20][21][22][23]), a notable application of quantum channel discrimination to a practical task as the memory readout. From this point of view, another well-known protocol is quantum illumination, which aims at improving target detection [25][26][27][28][29][30][31], and has been recently extended to its most natural domain, the microwaves [32].…”

Gaussian Hypothesis Testing and Quantum Illumination

“…The upshot is that quantum illumination can offer a significant performance advantage over a classical coherent-state transmitter of the same average photon number, when considering the sensing application mentioned above. To date, several experiments have been conducted that demonstrate the advantage quantum illumination offers [17][18][19][20].…”

Entanglement-enhanced Neyman–Pearson target detection using quantum illumination

“…As a result, the performance advantages of many entanglement-enabled sensing schemes-such as those that rely on frequency-entangled states (see, e.g., [1]), or N00N states (see, e.g., [2])-vanish as loss and noise increase. Quantum illumination (QI) [3][4][5][6][7][8][9][10], in contrast, is highly robust against environmental loss and noise. QI utilizes entanglement to beat the performance of the optimum classical-illumination (CI) scheme for detecting the presence of a weakly reflecting-target that is embedded in a very noisy environment, despite QI's initial entanglement being destroyed before the target-detection quantum measurement is made.…”