Time Entanglement between a Photon and a Spin Wave in a Multimode Solid-State Quantum Memory.

Kutlu Kutluer,Bernardo Casabone,Stefano Duranti,Margherita Mazzera,Emanuele Distante,Hugues De Riedmatten

doi:10.1103/physrevlett.123.030501

Abstract

The generation and distribution of entanglement are key resources in quantum repeater schemes. Temporally multiplexed systems offer time-bin encoding of quantum information which provides robustness against decoherence in fibers, crucial in long distance communication. Here, we demonstrate the direct generation of entanglement in time between a photon and a collective spin excitation in a rare earth ion doped ensemble. We analyze the entanglement by mapping the atomic excitation onto a photonic qubit and by using time-bin qubit analyzers implemented with another doped crystal using the atomic frequency comb technique. Our results provide a solid-state source of entangled photons with embedded quantum memory. Moreover, the quality of the entanglement is high enough to enable a violation of a Bell inequality by more than two standard deviations.

Highlights

Light-matter entanglement is an important resource in quantum information science
We demonstrate the direct generation of entanglement in time between a photon and a collective spin excitation in a rare earth ion doped ensemble
We analyze the entanglement by mapping the atomic excitation onto a photonic qubit and by using time-bin qubits analyzers implemented with another doped crystal using the atomic frequency comb technique

Summary

Experimental Setup

The AFC in the memory crystal is prepared with the read pulse mode. The read pulses have Gaussian amplitude modulation and a maximum power of 30 mW. They are 1 μs long and frequency chirped of 800 kHz with a hyperbolic tangent waveform. Both Stokes and anti-Stokes photons pass through the interferometric filter crystal (IFC), but in different spacial modes (about 4 mm apart), where dedicated laser beams prepare the required spectral features (transparency window or AFC). The total transmission in the Stokes (anti-Stokes) arm, from the cryostat to the detector, is typically 59 % (56 %), which takes into account the passive losses of the optical elements and the residual absorption in the IFC

Stokes creation probability

Coincidence histograms

Analysis of the CHSH inequality violation

Findings

Discussion on storage time and readout efficiency