Generation of Light with Multimode Time-Delayed Entanglement Using Storage in a Solid-State Spin-Wave Quantum Memory

Kate R. Ferguson, Sarah E. Beavan, Jevon J. Longdell, and Matthew J. Sellars

Phys. Rev. Lett. 117, 020501 – Published 6 July 2016

Abstract

Here, we demonstrate generating and storing entanglement in a solid-state spin-wave quantum memory with on-demand readout using the process of rephased amplified spontaneous emission (RASE). Amplified spontaneous emission (ASE), resulting from an inverted ensemble of $\Pr^{3 +}$ ions doped into a $Y_{2} {SiO}_{5}$ crystal, generates entanglement between collective states of the praseodymium ensemble and the output light. The ensemble is then rephased using a four-level photon echo technique. Entanglement between the ASE and its echo is confirmed and the inseparability violation preserved when the RASE is stored as a spin wave for up to $5 μ s$ . RASE is shown to be temporally multimode with almost perfect distinguishability between two temporal modes demonstrated. These results pave the way for the use of multimode solid-state quantum memories in scalable quantum networks.

Received 7 February 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.020501

Physics Subject Headings (PhySH)

Entanglement production Quantum communication Quantum information with solid state qubits Quantum memories

Rare-earth doped crystals

Quantum Information, Science & Technology

Authors & Affiliations

Kate R. Ferguson^1,*, Sarah E. Beavan², Jevon J. Longdell³, and Matthew J. Sellars¹

¹Centre for Quantum Computation and Communication Technology, Laser Physics Centre, Australian National University, Canberra, Australian Capital Territory 2601, Australia
²European Space Agency, NL-2200 AG, Noordwijk, The Netherlands
³Jack Dodd Centre for Photonics and Ultra-Cold Atoms, Department of Physics, University of Otago, Dunedin 9016, New Zealand

^*Corresponding author. katherine.ferguson@anu.edu.au

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Vol. 117, Iss. 2 — 8 July 2016

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Images

Figure 1
(a) RASE setup. The 0.005% Pr:YSO crystal, lens, and back mirror are located at the bottom of a liquid helium bucket cryostat at 4.2 K. The cryostat only has vertical optical access, so a top optics platform has fibre couplers steering the control and preparation beams into the cryostat and the reflected signal beam to the balanced heterodyne detection system. (b) Hyperfine levels of the ground ${}^{3}{H_{4}}$ and excited ${}^{1}{D_{2}}$ manifold in Pr:YSO. For the RASE experiment, a subensemble of ions is selected using spectral hole burning and prepared to be initially in state $| 1 ⟩$ . The frequencies used to apply the 4L-RASE protocol are marked. (c) Pulse sequence used in a single shot of the 4L-RASE experiment. After the inversion pulse $π_{inv}$ is applied, the ensemble is allowed to spontaneously emit for $T$ before the rephasing pulses $π_{1} = 1.5 μ s$ and $π_{2} = 2.2 μ s$ are applied. These are separated by a time $s$ , the storage time on the spin states. $A$ is the length of the ASE and RASE windows used for calculating the quadrature values. $B$ is the delay between the end (start) of the ASE (RASE) window and the rephasing pulses to allow the detectors to recover from saturation due to the intense $π$ pulses. After the sequence, two weak phase reference pulses, $ϕ_{1}$ and $ϕ_{2}$ , are applied to correct for the frequency dependent phase offsets shot to shot.
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Figure 2
(a) The cross-correlation function between the ASE and RASE fields [Eq. (1)] of the same shot, consecutive shots, and when the phase correction is not applied averaged over 8000 trials. (b) The inseparability criterion [Eq. (3)] as a function of $b$ when $s = 0$ . The ASE (RASE) variance is $1.453 \pm 0.023$ ( $1.015 \pm 0.016$ ) normalized to the vacuum. The shaded area indicates $1 σ$ confidence. Inset shows a close up of the minimum of the inseparability criterion.
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Figure 3
(a) $b$ and (b) the minimum inseparability violation with increasing spin-wave storage time $s$ . All error bars are $1 σ$ .
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Figure 4
(a) Pulse sequence used for the multimode 4L-RASE experiment showing the labeling of the two temporal modes. $A = 20 μ s$ , $B = 5 μ s$ , $T = 28.5 μ s$ , and $s = 0 μ s$ . (b) Inseparability criterion for the four combinations of the two temporal modes. The solid lines are the time-symmetric combinations showing a correlation. The dashed lines are the nonsymmetric cases and are uncorrelated. The shaded areas indicate $1 σ$ confidence. Inset shows a close up of the minimum of the criterion.
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