Quantum repeaters based on atomic ensembles and linear optics

Abstract

The distribution of quantum states over long distances is limited by photon loss. Straightforward amplification as in classical telecommunications is not an option in quantum communication because of the no-cloning theorem. This problem could be overcome by implementing quantum repeater protocols, which create long-distance entanglement from shorter-distance entanglement via entanglement swapping. Such protocols require the capacity to create entanglement in a heralded fashion, to store it in quantum memories, and to swap it. One attractive general strategy for realizing quantum repeaters is based on the use of atomic ensembles as quantum memories, in combination with linear optical techniques and photon counting to perform all required operations. Here we review the theoretical and experimental status quo of this very active field. We compare the potential of different approaches quantitatively, with a focus on the most immediate goal of outperforming the direct transmission of photons.

Towards an efficient atomic frequency comb quantum memory

“…quantum cryptography) and more generally for quantum networks. This can be achieved via so-called quantum repeaters [1,2,3,4], which can overcome the exponential transmission losses in optical fiber networks. Quantum memories (QM) for photons [5,6,7,8,9] are key components in quantum repeaters, because the distribution of entanglement using photons is of probabilistic nature due to the transmission losses over long quantum channels.…”

Generation of Narrow-Band Polarization-Entangled Photon Pairs at a Rubidium D1 Line

“…So our experimental setup is relative simple，which will benefit the practical application of entanglement source in quantum information process. The linewidth of polarization-entangled photon pairs here is 15 MHz, which matches the typical atomic memory bandwidth [2] 2. Experimental setup The experimental setup is shown in Fig.…”

Memory-assisted quantum key distribution resilient against multiple-excitation effects

“…We consider ensemble-based memories due to their strong light-matter coupling and, in several cases, the possibility of long coherence times (up to seconds [38]) and high bandwidths (up to several GHz [35]). Furthermore, they offer the possibility of multi-mode storage [7,11]. By multi-mode we are referring to memories that can simultaneously store more than one qubit during a single storage event by encoding many qubits each into a different mode.…”

“…The limitation in going to further distances is dictated by the exponentially-growing loss factor in optical fibers [3]. Probabilistic quantum repeaters offer a solution to extend the communication distance to over thousands of kilometers [4][5][6][7][8][9][10]. However, such quantum repeaters rely on quantum memory modules [11] with characteristics that are hard to achieve with the current technology.…”