Superdense Coding over Optical Fiber Links with Complete Bell-State Measurements

Abstract

Adopting quantum communication to modern networking requires transmitting quantum information through fiber-based infrastructure. We report the first demonstration of superdense coding over optical fiber links, taking advantage of a complete Bell-state measurement enabled by timepolarization hyperentanglement, linear optics, and common single-photon detectors. We demonstrate the highest single-qubit channel capacity to date utilizing linear optics, 1.665 ± 0.018, and we provide a full experimental implementation of a hybrid, quantum-classical communication protocol for image transfer.PACS numbers: 42.50. Ar,03.67.Bg,42.79.Sz Superdense coding enables one qubit to carry two bits of information between a sender Bob and receiver Alice when they share an entanglement resource, perhaps distributed at "off-peak" times [1]. Bob can choose to use this quantum ability at a time of optimal advantage, after the time of distribution, when he and Alice have access to quantum memory [2]. A significant challenge in realizing superdense coding is the need to perform a complete Bell-state measurement (BSM) on the photon pair, which is not possible using only linear optics and a single degree of shared entanglement [3,4]. While nonlinear optics [5] or utilization of ancillary photons and linear optics [6] enable a complete BSM, these methods are challenged by inefficiency and impracticality. However, a complete BSM with linear optics can be performed by using entanglement in additional degrees of freedom, so-called hyperentanglement [7,8]. Complete BSM implementations have been demonstrated previously using states hyperentangled in orbital angular momentum and polarization degrees of freedom [9] as well as with states hyperentangled in momentum and polarization [10]. However, these states are not compatible with transmission through fiber-based networks, which form the backbone of modern telecommunication systems. Previously, Schuck et al. have shown that timepolarization hyperentanglement can be used for complete and deterministic BSM [11], but required number resolving detectors to identify the states completely. Yet this encoding is attractive in that it permits efficient transmission through optical fiber and that some photon pair sources generate time entanglement for "free".In this article, we report results from an experimental demonstration of superdense coding over optical fiber links using a complete BSM based on time-polarization hyperentanglement. Our novel implementation requires only linear optics and common single-photon detectors. The resulting combination of a hyperentangled photon pair source and novel discrimination device yields an observed channel capacity of 1.665±0.018, the highest reported to date for a single-qubit and linear optics. We demonstrate the feasibility of this setup by transmitting a 3.4 kB image that is recovered with 87% fidelity. This FIG. 1: Our complete Bell state measurement is achieved using linear optics and time-polarization hyperentanglement. Two-photon interference is orchestrate...

The Linear Optical Unambiguous Discrimination of Hyperentangled Bell States Assisted by Time Bin

“…That is, the time interval between the wave packets of input state is adjusted to satisfy the condition of constructive interference with ωt = 2mπ (m is an integer), which has been demonstrated experimentally by Williams et al [33] In their experiment, the photon pairs prepared by SPDC are sent into an interferometer with two time delays t 0 = 5ns and t 1 = 10ns , and the time resolution for photon detectors is 4ns . That is, the time interval between the wave packets of input state is adjusted to satisfy the condition of constructive interference with ωt = 2mπ (m is an integer), which has been demonstrated experimentally by Williams et al [33] In their experiment, the photon pairs prepared by SPDC are sent into an interferometer with two time delays t 0 = 5ns and t 1 = 10ns , and the time resolution for photon detectors is 4ns .…”

“…In 2006, Schuck et al [25] gave the complete analysis of the four polarization Bell states in experiment with the help of the intrinsic time-energy correlation of photon pair. Recently, Williams et al [33] demonstrated an attractive protocol in experiment to completely differentiate the four polarization Bell states assisted by two time delays, where only www.advancedsciencenews.com www.ann-phys.org linear optical elements and common single-photon detectors are required. [26] with twophoton polarization-momentum hyperentanglement via linear optics.…”

“…[33] Ultimately, HWPs perform the Hadamard operations on the polarization modes of the two photons. [33] Ultimately, HWPs perform the Hadamard operations on the polarization modes of the two photons.…”

Advances in Quantum Dense Coding

“…Different complexities to realize these measurements made a big difference between the achieved results–the Illinois experiment achieved an average successful probability of 94.8% and a capacity of 1,630(6) bits thus beating a fundamental limit of log 2 3 bits on the dense coding capacity using only linear optics for the first time, while the Tianjin experiment observed an average success probability of and a capacity of 1.10(4) bits which is no better than the Innsbruck experiment . Time‐polarization hyperentanglement–based dense coding was further developed into the one using four temporal modes in the Oak Ridge experiment ( Figure ). This experiment achieved an average success probability of 95.3% and a capacity of 1.665(0.018) bits and, more importantly, paved the way for practical application of quantum dense coding for at least two reasons; first, its demonstration over optical fiber links can be easily extended to long distance communication assisted by quantum dense coding, secondly, it showed potential in hybrid quantum‐classical transfer protocols by transmitting a 3.4 kB image with 0.87 fidelity a.…”

“…Apparatus of Oak Ridge experiment . Four temporal modes were used to identify four Bell states without the requirement of PNRDs.…”