Cavity-enhanced storage in an optical spin-wave memory

Abstract

We report on the experimental demonstration of an optical spin-wave memory, based on the atomic frequency comb (AFC) scheme, where the storage efficiency is strongly enhanced by an optical cavity. The cavity is of low finesse, but operated in an impedance matching regime to achieve high absorption in our intrinsically low-absorbing Eu 3+ :Y 2 SiO 5 crystal. For storage of optical pulses as an optical excitation (AFC echoes), we reach efficiencies of 53% and 28% for 2 μs and 10 μs delays, respectively. For a complete AFC spin-wave memory we reach an efficiency of 12%, including spin-wave dephasing, which is a 12-fold increase with respect to previous results in this material. This result is an important step towards the goal of making efficient and long-lived quantum memories based on spin waves, in the context of quantum repeaters and quantum networks.

Spectral Multiplexing for Scalable Quantum Photonics using an Atomic Frequency Comb Quantum Memory and Feed-Forward Control

“…Finally, in regards to the AFC itself, the quantum memory protocol theoretically allows for 100% efficiency [23]. Improvements from our current 1% rely on increased comb contrast and comb finesse F = ∆/γ (where ∆ is the teeth spacing and γ is the linewidth of each tooth [23]), and the preparation of a spatio-spectral grating [40] or embedding of the rare-earth-ion-doped crystal into an impedance-matched cavity [20,37,41,42]. We note that the possibility to increase the finesse, as well as to achieve longer storage times, relies on minimizing the parameters ∆ and γ.…”

“…Realizing temporal multiplexing with recall on demand in AFC memories requires mapping of optically excited coherence onto long lived ground state coherence (often called spin-wave mapping see [21,[35][36][37] for recent progress). Please recall that the maximal bandwidth of a high-efficiency AFC is determined by the ground-level splitting, which is around 10 MHz in the materials used to date to implement the protocol (much less than 300 GHz, as needed for repeater performance comparable with that derived above for a spectral-multiplexing-based architecture).…”

Multiresonator quantum memory

“…The impedance condition physically adjusts the optimal interference effects of the light media interaction in the resonant cavities that significantly facilitates the implementation of the main requirements to the quantum dynamics of light. First experiments of the impedance matched photon echo QM schemes have been successfully demonstrated in the optical cavities [23][24][25].…”

“…This happens due to the impedance matching enhancement of the resonant interaction of a weak signal light field with a small number of atoms [21][22][23][24][25][26]. However, this impedance matching scheme has a limited spectral range, since its range is determined by the quality factor of the resonator [22,27,28].…”

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

“…On-demand storage at the single photon level is shown in [41], in which dynamical decoupling techniques are also used to overcome dephasing due to spin inhomogeneous broadening. Reference [42] utilizes a low-finesse cavity to show (up to 50%) efficient and on-demand storage of strong pulses. Efficient storage using a low-finesse cavity is achieved in [43], while on-demand storage of qubits and heralded single photons are shown in [44,45], respectively.…”