Storage of photonic time-bin qubits for up to 20 ms in a rare-earth doped crystal

Abstract

Long-duration quantum memories for photonic qubits are essential components for achieving longdistance quantum networks and repeaters. The mapping of optical states onto coherent spin-waves in rare earth ensembles is a particularly promising approach to quantum storage. However, it remains challenging to achieve long-duration storage at the quantum level due to read-out noise caused by the required spin-wave manipulation. In this work, we apply dynamical decoupling techniques and a small magnetic field to achieve the storage of six temporal modes for 20, 50 and 100 ms in a 151 Eu 3+ :Y2SiO5 crystal, based on an atomic frequency comb memory, where each temporal mode contains around one photon on average. The quantum coherence of the memory is verified by storing two time-bin qubits for 20 ms, with an average memory output fidelity of F = (85 ± 3) % for an average number of photons per qubit of µ = 0.92±0.04. The qubit analysis is done at the read-out of the memory, using a novel composite adiabatic read-out pulse.

A readout-integrated time-bin qutrit analyzer for echo-based quantum memories

“…To perform two successive partial readouts despite these constraints we previously have proposed and implemented a composite pulse for analyzing time-bin qubits [16]. We extend this approach to the three partial readouts that are necessary to analyze qutrits and take the opportunity to have a closer look at its performance in a Maxwell-Bloch simulation.…”

“…After being mapped to the spin transition, the coherence is stored there for 20 ms. To preserve coherence, we perform a single XY4 decoupling sequence [44]. Additionally, during the whole experiment we apply a static magnetic field of 1.35 mT along the D 1 -axis of the crystal which has been shown to increase the coherence time of the spin transition significantly [16,45]. A more detailed description of this setup and a characterization of its performance as a memory platform can be found in Ref.…”

“…A more detailed description of this setup and a characterization of its performance as a memory platform can be found in Ref. [16]. the retrieval of the coherence we finally apply a pulse that implements the desired PRA.…”

“…A suitable candidate for implementing high dimensional photonic quantum states are time-bin qudits. For these, entangled states can be readily generated [11,12], and temporally multimode quantum memories can be used for their storage [13][14][15][16]. For time-bin qubits it has been demonstrated that in certain types of echobased optical memories, projective measurements can be conveniently integrated into the readout process [17][18][19].…”

Optimization and readout-noise analysis of a warm vapor EIT memory on the Cs D1 line

“…These act as interfaces between flying and stationary qubits and allow for storage of quantum information, ideally in an efficient and noise-free manner. QMs are being developed in many different platforms, ranging from ultracold atoms [14][15][16] to solid-state systems [17][18][19][20][21] and warm atomic vapors [22][23][24][25][26]. The latter constitute technologically simple and scalable systems.…”