P. Goiporia | Searcharxiv

arXiv2024

A universal neutral-atom quantum computer with individual optical addressing and non-destructive readout

Quantum computers must achieve large-scale, fault-tolerant operation to deliver on their promise of transformational processing power [1-4]. This will require thousands or millions of high-fidelity quantum gates and similar numbers of qubits [5]. Demonstrations using neutral-atom qubits trapped and manipulated by lasers have shown that this modality can provide high two-qubit gate (CZ) fidelities and scalable operation [6-13]. However, the gates in these demonstrations are driven by lasers that do not resolve individual qubits, with universal computation enabled by physical mid-circuit shuttling of the qubits. This relatively slow operation may greatly extend runtimes for useful, large-scale computation. Here we demonstrate a universal neutral-atom quantum computer with gate rates limited by optical switching times, rather than shuttling, by individually addressing tightly focused laser beams at an array of single atoms. We achieve CZ fidelity of 99.35(4)% and local single-qubit RZ gate fidelity of 99.902(8)%. Moreover, we demonstrate non-destructive readout of alkali-atom qubits with 0.9(3)% loss, which boosts operational speed. This technique also enables us to measure a state-of-the-art CZ fidelity of 99.73(3)% when excluding atom-loss events, which may be mitigated through erasure conversion. Our results represent a critical step towards large-scale, fault-tolerant neutral-atom quantum computers that can execute computations on practical timescales.

quant-ph↗

arXiv2022

SupercheQ: Quantum Advantage for Distributed Databases

We introduce Supercheq, a family of quantum protocols that achieves asymptotic advantage over classical protocols for checking the equivalence of files, a task also known as fingerprinting. The first variant, Supercheq-EE (Efficient Encoding), uses $n$ qubits to verify files with $2^{O(n)}$ bits -- an exponential advantage in communication complexity (i.e.~bandwidth, often the limiting factor in networked applications) over the best possible classical protocol in the simultaneous message passing setting. Moreover, Supercheq-EE can be gracefully scaled down for implementation on circuits with $\mathrm{poly}(n^\ell)$ depth to enable verification for files with $O(n^\ell)$ bits for arbitrary constant $\ell$. The quantum advantage is achieved by random circuit sampling, thereby potentially endowing circuits from recent quantum supremacy and quantum volume experiments with a practical application. We validate Supercheq-EE's performance at scale through GPU simulation motivated by Infleqtion's Sqale neutral atom QPU gateset. The second variant, Supercheq-IE (Incremental Encoding), also achieves arbitrary-polynomial advantage in fingerprint size ($n$ qubits to verify files with size $O(n^{\ell})$ bits), while supporting incremental updates to the fingerprint using only a constant number of $(\ell-1)$-qubit gates. Moreover, Supercheq-IE at $\ell=2$ ($\geq 3$) only requires Clifford gates (gates in the $\ell-1$ level of the Clifford hierarchy), ensuring relatively modest overheads for error-corrected implementation. We experimentally demonstrate proof-of-concepts on quantum hardware from Diraq (spin qubit) and IBM (superconducting). We envision Supercheq could be deployed in distributed data settings, accompanying replicas of important databases.

quant-ph↗