Quantum Memory Channels in Quantum Optics

Tomáš Rybár, Mário Ziman, Vladimír Bužek

P. Ben Dixon, Ryan P. Murphy, Matthew E. Grein +11 more

We report on the engineering of a multi-qubit silicon-vacancy-based quantum memory module suitable for quantum networking over optical channels.

Harry J. Kimble

Alexander I. Lvovsky, Barry C. Sanders, Wolfgang Tittel

Prajit Dhara, Liang Jiang, Saikat Guha

Entangling quantum memories, mediated by optical-frequency or microwave channels, at high rates and fidelities is key for linking qubits across short and long ranges. All well-known protocols encode up to one qubit per optical mode, entangling one pair of memory qubits per transmitted mode over the channel, with probability η, the channel’s transmissivity. The rate is proportional to η ideal Bell states (ebits) per mode. The quantum capacity, C(η)=−log2⁡(1−η) ebits per mode, which ≈1.44η for high loss, thereby making these schemes near rate-optimal. However, C(η)→∞ as η→1, making the known schemes highly rate-suboptimal for shorter ranges. We propose a cavity-assisted memory–photon interface that can be used to entangle matter memories with Gottesman–Kitaev–Preskill (GKP) photonic qudits, which, along with dual-homodyne entanglement swaps that retain analog information, enables entangling memories at capacity-approaching rates at low loss. We benefit from the loss resilience of GKP-encoded states and the ability to encode multiple qubits in one mode. Our memory–photon interface further supports the preparation of needed ancilla GKP qudits. We expect our result to spur research in low-loss, high-cooperativity cavity-coupled qubits with high-efficiency optical coupling and demonstrations of high-rate short-range quantum links.

D O Akat’ev, А. А. Калачев

Abstract We consider preparing entangled states between single photons and quantum memory by combining two-photon source based on spontaneous parametric down-conversion and multiatomic quantum memory in a common resonator. The scheme allows one to minimize the losses while the photon to be stored is propagating from the source to the quantum memory and avoids the need to synchronize their operating wavelength. In this respect, the scheme is analogous to the cavity-enhanced embedded memory within Duan-Lukin-Cirac-Zoller approach, but it remains possible to generate a second photon at the wavelength of the fiber optic communication channel and use various multiplexing methods inherent in multiatomic quantum memory.