Quantum receiver for phase-shift keying at the single photon level

Abstract

Quantum enhanced receivers are endowed with resources to achieve higher sensitivities than conventional technologies. For application in optical communications, they provide improved discriminatory capabilities for multiple nonorthogonal quantum states. In this work, we propose and experimentally demonstrate a new decoding scheme for quadrature phase-shift encoded signals. Our receiver surpasses the standard quantum limit and outperforms all previously known nonadaptive detectors at low input powers. Unlike existing approaches, the receiver only exploits linear optical elements and on-off photodetection. This circumvents the requirement for challenging feed-forward operations that limit communication transmission rates and can be readily implemented with current technology.

Advances in space quantum communications

“…Second, on the receiver side, large diameter receiver apertures coupled to efficient detection systems are required to recover the faint, quantum signals from space. Incorporating methods from quantum detection theory benefit the channel capacity [17]. Finally, probes in deep space have a smaller communication window than near‐Earth probes, owing to an increased duration of the probe orbits within near‐sun angles [167].…”

“…A number of technologies can inherit enhanced performances and securities when availed to quantum mechanical resources. These technologies include sensing [8–10], metrology [11–13], navigation and timing [14], state discrimination [15–17], communication [18, 19] and computation [20]. Today, these technologies have long evolved from theoretical curiosities to significant developments and even field realisations.…”

Unambiguous discrimination of coherent states

“…Hence, coherent states cannot be discriminated with zero probability of error. There is an extensive body of research on receiver designs that distinguish coherent states [8][9][10][11]. The so-called Dolinar receiver [12], which employs a local-oscillator laser, and electro-optic modulator, shotnoise photon detection and electro-optic feedback, can achieve the Helstrom limit for discriminating any two coherent states.…”

Experimental multi-state quantum discrimination through a Quantum network

“…The quest for effective protocols has led to many results concerning optimal theoretical bounds and optimal receiver models for binary discrimination in different contexts [5,[10][11][12]. On the other hand, regarding the general case of multiple states and dimension D > 2, definitive results have not been achieved yet; while the optimal one-shot bound has been set [11], many attempts have been done to develop new and more effective strategies using adaptive protocols [13][14][15][16] or auxiliary systems [17]. Other proposals involve the exploitation of an auxiliary system [18], in order to increase the dimension of the system to be discriminated, or consist of encoding the states in a complex modal structure [19].…”

“…In this scenario, optimal strategies for Quantum State Discrimination of actual quantum states have a great deal of relevance and a wide range of applications: Quantum Communication [26], Quantum Key Distribution [27] and also Quantum Sensing, in the case of distinguishing different external fields affecting the system dynamics (such as in NV-center noise spectroscopy [28] or avian magnetoreception [29]). In recent years the development of actual single-photon protocols for QSD has been quite rare, while a lot of effort has been spent in developing protocols requiring the exploitation of coherent states (adaptive strategies, Quantum Phase Shift Keying [13][14][15]17]). However, it is well known that the use of coherent states in Quantum Communication protocols does not grant equal security as compared to the exploitation of actual quantum states.…”