Robust multi-qubit quantum network node with integrated error detection

Abstract

Long-distance quantum communication and networking require quantum memory nodes with efficient optical interfaces and long memory times. We report the realization of an integrated two-qubit network node based on silicon-vacancy centers (SiVs) in diamond nanophotonic cavities. Our qubit register consists of the SiV electron spin acting as a communication qubit and the strongly coupled silicon-29 nuclear spin acting as a memory qubit with a quantum memory time exceeding 2 seconds. By using a highly strained SiV, we realize electron-photon entangling gates at temperatures up to 1.5 kelvin and nucleus-photon entangling gates up to 4.3 kelvin. We also demonstrate efficient error detection in nuclear spin–photon gates by using the electron spin as a flag qubit, making this platform a promising candidate for scalable quantum repeaters.

Performance analysis of quantum repeaters enabled by deterministically generated photonic graph states

“…For example, the feedback-assisted generation scheme should be preferred for systems possessing a large oscillator strength that can exhibit a large radiative emission rate to a specific waveguide or cavity mode, such as self-assembled quantum dots [34,50,51], silicon-vacancy (SiV) centers in diamond [35], or atomic ensembles where superradiance can be employed [52]. Other atomic systems, such as trapped neutral atoms [26,53], rare-earth ion impurities [36,37], or many quantum defect centers [54], in general possess weaker radiative decay rates and therefore may be more suited for the ancillary-qubit-assisted scheme, especially if they can be easily coupled to nearby nuclear spins, which can serve as the ancillary matter qubits [43,46,55,56].…”

“…o Entanglement of two spin qubits can be realized through their local dipolar interactions, which are typically weak, ranging from hundreds of kHz to a few hundreds MHz. For example, the hyperfine interaction strength between an electron spin of a nitrogen-vacancy (NV) center in diamond and a nearby 13 C or 14 N nuclear spin is around 10 MHz [43,44], and the hyperfine interaction strength in a silicon-vacancy (SiV) center in diamond is a few MHz between an electron spin and a carbon-13 nuclear spin [45] and a few hundreds MHz between an electron spin and a 29 Si nuclear spin [46]. Composite microwave pulses can be employed to realize high-fidelity entangling gates, resulting in a gate time of at least hundreds of nanoseconds [47].…”

What are the ultimate limits of photonic quantum memories?

“…Photonic quantum memories are required in many applications in quantum information science with varying performance requirements depending on specific applications. Although classical light storage has been demonstrated in time scales of minutes (Dudin and Kuzmich, 2013;Heinze et al, 2013) to hours (Ma et al, 2021) in different systems, storing true single photons and single photon level coherent pulses are still limited to around a few seconds at most (Wang et al 2021;Ortu et al, 2022;Hain et al, 2022;Stas et al 2022). In this question we would like to explore what the challenges for quantum memory storage for the purposes of quantum communication and the distribution of entanglement are, e.g.…”

Long-lived entanglement memory in a trapped-ion quantum network node

“…The ideal iSWAP performs the mapping φ N ⊗ ↓ L → ↓ N ⊗ φ L , where φ is the arbitrary state to be swapped to the logic qubit, leaving the network qubit in the ↓ N state. Experimental imperfections leading to deviations from the target subspace ↓ N ↓ N ⊗ 1L are detected via a mid-circuit measurement on the network qubit [46]. We characterize the iSWAP operation independently using process tomography [47,48] to reconstruct the Choi…”