Recent experiments have demonstrated the strain-mediated driving of an AA electron spin ground state with a classical phonon field 44, 45. As compared to optomechanical 40, 41, 42 and electro-optical 43 transduction schemes, quantum teleportation circumvents the direct conversion of quantum states into photons and thus minimizes the infidelity associated with undetected (unheralded) photon loss. The last mentioned, optical response of AAs conditioned on the electron spin state, can be used to generate heralded entanglement 14, 38, 39 and thus allow for networking (e.g., connecting the device to the quantum internet) via quantum-state teleportation. Previous work has investigated these quantum interfaces separately, including the piezoelectric transduction from the microwave circuit to the phonon 12, 15, 16, 17, 18, 19, 20, 21, spin-strain coupling in solid-state quantum emitters 10, 11, 22, 23, 24, 25, 26, 27, 28, hyperfine interactions of electron spins with nearby nuclei 13, 29, 30, 31, 32, 33, and spin-dependent optical transitions 34, 35, 36, 37. 1, combines four quantum interfaces between physical modalities: a microwave photon-to-phonon interface, coupling of a phonon to an AA electron spin, coupling of the electron spin to a nuclear spin, and finally coupling of the electron spin to the optical photon. Our approach, schematically depicted in Fig. By combining the complementary strengths of SC circuit quantum computing and artificial atoms, this hybrid SC-AA architecture has the essential elements for extensible quantum information processors: a high-fidelity quantum processing unit (QPU), a bus to scalable quantum memory, and a high-fidelity connection long-range optical quantum networks. Noting that SiV − single-shot optical readout fidelity has been experimentally demonstrated to exceed 99.9% 14, this approach thus successfully addresses challenges (i-iv). Moreover, the scheme is extensible to large numbers of spin qubits with deterministic addressability, potentially enabling integration of large-scale quantum memory. Hyperfine coupling to local 13C nuclear-spin qubits enables coherence times exceeding a minute 13, while excited orbital states enable long-distance state transfer across quantum networks by optically heralded entanglement. Applied to present-day experimental parameters for SC flux qubits and silicon-vacancy (SiV −) centers in diamond, we estimate quantum state transfer with fidelity exceeding 99% at a MHz-scale bandwidth. Mediating this transduction is an acoustic bus 9, 10, 11, 12 that couples to the SC qubit and an AA electron spin via a combination of piezoelectric transduction and strong spin-strain coupling.
Here, we propose an approach to enable such scalable solid-state quantum computing platforms, based fundamentally on a mechanism for high-fidelity qubit transduction between an SC circuit and a solid-state artificial atom (AA). A hybrid system may satisfy these challenges by delegating different tasks to constituent physical platforms.
In particular, while superconducting (SC) circuits have high-fidelity and high-speed initialization and logic gates 1, 2, 3, 4, 5, 6, 7, 8, challenges remain in improving qubit (i) coherence times, (ii) long-range connectivity, (iii) qubit number, and (iv) readout fidelity.
Hybrid quantum systems have the potential to optimally combine the unique advantages of disparate physical qubits.
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