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arXiv:1504.02220 · Physical Review A

Storage and retrieval of microwave fields at the single-photon level in a spin ensemble

Cécile Grèzes, Brian Julsgaard, Yuimaru Kubo, Wen-Long Ma, Michael Stern, Audrey Bienfait, Kazuo Torii Nakamura, Junichi Isoya, Shinobu Onoda, Takeshi Ohshima, V. Jacques, D. Vion, D. Esteve, Ren‐Bao Liu, Klaus Mølmer, Patrice Bertet

Published Aug 7, 2015• 62 citations
arXivHTMLPDF

Abstract

We report the storage of microwave pulses at the single-photon level in a spin-ensemble memory consisting of ${10}^{10}$ nitrogen-vacancy centers in a diamond crystal coupled to a superconducting $LC$ resonator. The energy of the signal, retrieved $100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ later by spin-echo techniques, reaches $0.3%$ of the energy absorbed by the spins. This $0.3%$ storage efficiency is quantitatively accounted for by simulations. This figure of merit is sufficient to envision first implementations of a quantum memory for superconducting qubits.

DOI
10.1103/physreva.92.020301

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We report the storage of microwave pulses at the single-photon level in a spin-ensemble memory consisting of 1010{10}^{10}1010 nitrogen-vacancy centers in a diamond crystal coupled to a superconducting LCLCLC resonator. The energy of the signal, retrieved 100\ensuremathμs100\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}100\ensuremathμs later by spin-echo techniques, reaches 0.30.3%0.3 of the energy absorbed by the spins. This 0.30.3%0.3 storage efficiency is quantitatively accounted for by simulations. This figure of merit is sufficient to envision first implementations of a quantum memory for superconducting qubits.
A quantum memory at microwave frequencies, able to store the state of multiple superconducting qubits for long times, is a key element for quantum information processing. Electronic and nuclear spins are natural candidates for the storage medium as their coherence time can be well above one second. Benefiting from these long coherence times requires to apply the refocusing techniques used in magnetic resonance, a major challenge in the context of hybrid quantum circuits. Here we report the first implementation of such a scheme, using ensembles of nitrogen-vacancy (NV) centres in diamond coupled to a superconducting resonator, in a setup compatible with superconducting qubit technology. We implement the active reset of the NV spins into their ground state by optical pumping and their refocusing by Hahn echo sequences. This enables the storage of multiple microwave pulses at the picoWatt level and their retrieval after up to 35μ35 μ35μs, a three orders of magnitude improvement compared to previous experiments.
This article reviews efforts to build a new type of quantum device, which combines an ensemble of electronic spins with long coherence times, and a small-scale superconducting quantum processor. The goal is to store over long times arbitrary qubit states in orthogonal collective modes of the spin-ensemble, and to retrieve them on-demand. We first present the protocol devised for such a multi-mode quantum memory. We then describe a series of experimental results using NV (as in nitrogen vacancy) center spins in diamond, which demonstrate its main building blocks: the transfer of arbitrary quantum states from a qubit into the spin ensemble, and the multi-mode retrieval of classical microwave pulses down to the single-photon level with a Hahn-echo like sequence. A reset of the spin memory is implemented in-between two successive sequences using optical repumping of the spins.
We propose a multimode quantum memory protocol able to store the quantum state of the field in a microwave resonator into an ensemble of electronic spins. The stored information is protected against inhomogeneous broadening of the spin ensemble by spin-echo techniques resulting in memory times orders of magnitude longer than previously achieved. By calculating the evolution of the first and second moments of the spin-cavity system variables for current experimental parameters, we show that a memory based on nitrogen vacancy center spins in diamond can store a qubit encoded on the |0> and |1> Fock states of the field with 80% fidelity and outperform classical memory strategies for storage times ≤69 μs.
We describe a multi-mode quantum memory for propagating microwave photons that combines a solid-state spin ensemble resonantly coupled to a frequency tunable single-mode microwave cavity. We first show that high efficiency mapping of the quantum state transported by a free photon to the spin ensemble is possible both for strong and weak coupling between the cavity mode and the spin ensemble. We also show that even in the weak coupling limit unit efficiency and faithful retrieval can be obtained through time reversal inhomogeneous dephasing based on spin echo techniques. This is possible provided that the cavity containing the spin ensemble and the transmission line are impedance matched. We finally discuss the prospects for an experimental implementation using a rare-earth doped crystal coupled to a superconducting resonator.
We describe a multi-mode quantum memory for propagating microwave photons that combines a solid-state spin ensemble resonantly coupled to a frequency tunable single-mode microwave cavity. We first show that high efficiency mapping of the quantum state transported by a free photon to the spin ensemble is possible both for strong and weak coupling between the cavity mode and the spin ensemble. We also show that even in the weak coupling limit unit efficiency and faithful retrieval can be obtained through time reversal inhomogeneous dephasing based on spin echo techniques. This is possible provided that the cavity containing the spin ensemble and the transmission line are impedance matched. We finally discuss the prospects for an experimental implementation using a rare-earth doped crystal coupled to a superconducting resonator.