Verifiable Blind Quantum Computing with Trapped Ions and Single Photons
Physical Review Letters American Physical Society (APS) 132:15 (2024) 150604
Breaking the Entangling Gate Speed Limit for Trapped-Ion Qubits Using a Phase-Stable Standing Wave.
Physical review letters American Physical Society (APS) 131:22 (2023) 220601
Abstract:
All laser-driven entangling operations for trapped-ion qubits have hitherto been performed without control of the optical phase of the light field, which precludes independent tuning of the carrier and motional coupling. By placing ^{88}Sr^{+} ions in a λ=674 nm standing wave, whose relative position is controlled to ≈λ/100, we suppress the carrier coupling by a factor of 18, while coherently enhancing the spin-motion coupling. We experimentally demonstrate that the off-resonant carrier coupling imposes a speed limit for conventional traveling-wave Mølmer-Sørensen gates; we use the standing wave to surpass this limit and achieve a gate duration of 15 μs, restricted by the available laser power.Robust quantum memory in a trapped-ion quantum network node
Physical Review Letters American Physical Society 130 (2023) 090803
Abstract:
We integrate a long-lived memory qubit into a mixed-species trapped-ion quantum network node. Ion-photon entanglement first generated with a network qubit in 88Sr+ is transferred to 43Ca+ with 0.977(7) fidelity, and mapped to a robust memory qubit. We then entangle the network qubit with another photon, which does not affect the memory qubit. We perform quantum state tomography to show that the fidelity of ion-photon entanglement decays ∼ 70 times slower on the memory qubit. Dynamical decoupling further extends the storage time; we measure an ion-photon entanglement fidelity of 0.81(4) after 10 s.Experimental quantum key distribution certified by Bell's theorem
Nature Springer Nature 607:7920 (2022) 682-686
Abstract:
Cryptographic key exchange protocols traditionally rely on computational conjectures such as the hardness of prime factorization<sup>1</sup> to provide security against eavesdropping attacks. Remarkably, quantum key distribution protocols such as the Bennett-Brassard scheme<sup>2</sup> provide information-theoretic security against such attacks, a much stronger form of security unreachable by classical means. However, quantum protocols realized so far are subject to a new class of attacks exploiting a mismatch between the quantum states or measurements implemented and their theoretical modelling, as demonstrated in numerous experiments<sup>3-6</sup>. Here we present the experimental realization of a complete quantum key distribution protocol immune to these vulnerabilities, following Ekert's pioneering proposal<sup>7</sup> to use entanglement to bound an adversary's information from Bell's theorem<sup>8</sup>. By combining theoretical developments with an improved optical fibre link generating entanglement between two trapped-ion qubits, we obtain 95,628 key bits with device-independent security<sup>9-12</sup> from 1.5 million Bell pairs created during eight hours of run time. We take steps to ensure that information on the measurement results is inaccessible to an eavesdropper. These measurements are performed without space-like separation. Our result shows that provably secure cryptography under general assumptions is possible with real-world devices, and paves the way for further quantum information applications based on the device-independence principle.Position Measurement of a Levitated Nanoparticle via Interference with Its Mirror Image.
Physical review letters 129:1 (2022) 013601