Telecom-Wavelength Atomic Quantum Memory in Optical Fiber for Heralded Polarization Qubits

Abstract

Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this platform, including sources of entangled photons, efficient single photon detectors, and on-chip quantum circuits, a missing element has been atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of a telecom-wavelength photon. Here we demonstrate the quantum storage and retrieval of polarization states of heralded single-photons at telecom-wavelength by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing.Photonic quantum communication technologies rely on encoding quantum information (e.g. qubits) into single photons, and processing and distributing it to distant locations. In principle, a qubit can be encoded into any photonic degree of freedom, but the polarization degree has often been a preferred choice due to the ease of performing single qubit manipulations and projection measurements using wave-plates and polarizing beamsplitters, and the availability of polarization-entangled photon-pair sources [1]. On this background many seminal demonstrations of quantum information processing have employed polarization qubits, such as teleportation [2], entanglement swapping [3], and secure quantum key distribution over more than hundred kilometers [4], pointing towards the possibility to build secure quantum networks [5].In addition to polarization encoding, the realization of future quantum networks will be greatly facilitated by the use of existing fiber optic infrastructure, which allows low propagation loss for photons at wavelengths around 1550 nm, commonly referred to as telecom-wavelengths [6]. Nevertheless, propagation loss still limits the distance of such quantum links to a few hundreds kilometers. This distance barrier may be overcome by the development of quantum repeaters [7]. These, in turn, rely on the ability to store photonic qubits in quantum memories to overcome the probabilistic nature of photon transmission through lossy quantum channels and emission from cur- † J.J. and E.S. contributed equally to this work.rently used single-photon sources [8,9]. However, to date, no quantum memory for polarization qubits encoded into telecom wavelength photons has been demonstrated. In fact, until recently [18], direct quantum storage of telecom-wavelength photons was an unsolved problem. The most promising candidate, erbium, has the required transition wavelength but exhib...

Fiber entangled photon pair source connecting telecom to quantum memories

“…For case (a) the g 2 ( ) and coincidence rates for the specific wavelengths of imply quantum non-classicality and entanglement [23][24][25]. Currently Erbium memories have been experimentally demonstrated as feasible in the 1-100 GHz ranges or more though with reduced efficiency beyond~10 GHz [33]. As will be discussed below most diamond memories demonstrated have been in the MHz bandwidth range except for the recent GHz bandwidth demonstration for SiV [34].…”

“…In crystals like Er:YSO storage times up to 20 ms [40] are possible but the bandwidth is limited to 100s of MHz [41]. To partially overcome the bandwidth limitation Er doped fibers have been explored [33]. They have demonstrated broad bandwidths on the order of 8 GHz (full inhomogeneous bandwidth >1 THz) which are a better match for the short pulses desired in future QC systems.…”

“…They can also have a large time-bandwidth product, in excess of 100, and so can store many quantum optical modes. Current weaknesses are short storage times (~5 ns) and low efficiencies (~1%) [33].…”

Serialized quantum error correction protocol for high-bandwidth quantum repeaters

“…The pulse duration of the input photon in the strong coupling regime is limited by the coupling strength to t p = ( ) g 1 2 =8 ps [46], thus providing the possibility for both high fidelity and gigahertz bandwidths. Though operation at these simultaneously high cooperativities and gate speeds have not been directly demonstrated at telecom wavelengths, there have been a few quantum dot and atomic systems resonant in this band of frequencies that could be potentially considered for such use [55,56].…”

Multiplexed entangled photon-pair sources for all-fiber quantum networks

“…Also significant progresses in suppressing the intense Raman scattering noise of photon pair generating in DSF have been achieved by using pulse pumping, polarization filtering, high performance superconducting nanowire single photon detectors for time filtering and cooling with liquid gasses [22,23], the coincidence to accidental coincidence ratio is increased to very high level, which is feasible to be used in quantum information processing task. Very recently, ground break works on quantum storage of telecom band photonic polarization qubit, time-bin entangled state and frequency multiplexed modes in erbium doped optical fiber are demonstrated [24][25][26], which show great potential for implementing a long distance all fiber quantum networks. All fiber entangled photon sources are good candidate for achieving this goal.…”