New advances promise secure quantum computing at home
This advance promises to unlock the transformative potential of cloud-based quantum computing and is detailed in a new study published in Physical Review ...
published
The full power of next-generation quantum computing could soon be harnessed by millions of individuals and companies, thanks to a breakthrough by scientists at Oxford University Physics guaranteeing security and privacy. This advance promises to unlock the transformative potential of cloud-based quantum computing and is detailed in a new study <anchor>published</anchor> in Physical Review Letters. The paper is titled "Verifiable blind quantum computing with trapped ions and single photons."
Phys. Rev. Lett. 132, 150604 (2024) - Verifiable Blind Quantum Computing with Trapped Ions and Single Photons
## Physical Review Letters

### Verifiable Blind Quantum Computing with Trapped Ions and Single Photons

##### P. Drmota, D. P. Nadlinger, D. Main, B. C. Nichol, E. M. Ainley, D. Leichtle, A. Mantri, E. Kashefi, R. Srinivas, G. Araneda, C. J. Ballance, and D. M. Lucas

##### Phys. Rev. Lett. 132, 150604 – Published 10 April 2024

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#### Abstract

We report the first hybrid matter-photon implementation of verifiable blind quantum computing. We use a trapped-ion quantum server and a client-side photonic detection system networked via a fiber-optic quantum link. The availability of memory qubits and deterministic entangling gates enables interactive protocols without postselection—key requirements for any scalable blind server, which previous realizations could not provide. We quantify the privacy at ≲0.03 leaked classical bits per qubit. This experiment demonstrates a path to fully verified quantum computing in the cloud.

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- Received 10 May 2023

- Accepted 16 January 2024

DOI:https://doi.org/10.1103/PhysRevLett.132.150604



Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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#### Physics Subject Headings (PhySH)

1. Research Areas

Quantum Information, Science & Technology

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#### Cloud Computing under the Cover of Quantum

###### Published 21 May 2024

A secure method for cloud-based quantum computing harnesses the power of quantum physics to keep data confidential.

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#### Authors & Affiliations

- 1Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
- 2Laboratoire d’Informatique de Paris 6, CNRS, Sorbonne Université, Paris 75005, France
- 3Joint Center for Quantum Information and Computer Science, University of Maryland, College Park, Maryland, USA
- 4School of Informatics, University of Edinburgh, Edinburgh EH8 9AB, United Kingdom

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- ###### Figure 1

Verifiable blind quantum computing in the measurement-based model. The computation is expressed as a sequence of measurements on a brickwork state (two-dimensional graph with vertices representing virtual qubits, and edges indicating cz gates). The server holds m physical memory qubits (orange atoms) and one physical network qubit (violet atom). The server can entangle these qubits deterministically with each other. The network qubit can also be entangled with a photon; by measuring this photon, the client can steer the network qubit in the server remotely without the server learning about its state. This allows the client to hide the computation (inputs, outputs, and circuit) from the server. Moreover, the client can verify that the computation has not been tampered with by (randomly) interleaving test rounds, which produce classically simulatable outcomes and cannot be distinguished from the actual computation by the server.

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- ###### Figure 2

Protocol used to generate a linear cluster state using a trapped-ion quantum server and a photonic client. The client can steer the network qubit into |θℓ⟩=|θ˜ℓ+cℓπ⟩ by measuring the polarization of the photon in the basis B^θ˜ℓ and obtaining cℓ∈{0,1} as outcome. In the initialization step, the server transfers this state onto a memory qubit such that the network qubit can be steered again [ 21]. Every subsequent interaction step extends the size of the cluster state; the client steers the network qubit remotely into |θℓ+1⟩, the server entangles it (cz gates), and performs a measurement in the basis B^δℓ, where δℓ is provided by the client. See text for details.

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- ###### Figure 3

The client performs remote state preparation (RSP) using a fast-switching polarization analyzer. (a) The control voltages (Ua, Ub) of two EOMs separated by a λ/4 wave plate enable the client to arbitrarily rotate the measurement basis given by the PBS. (b) Laser light is used to reconstruct this basis for different Ua, Ub. Polarization ellipses are shown for the basis states heralded by detector p, where the color represents their phase. (c) To find Ua, Ub which maximize the fidelity F to each target state needed during the protocol, we perform tomography on the network qubit after RSP. The averaged results from 36 calibrations over 2 weeks are shown in the Bloch sphere representation of the network qubit. Values indicate F, with standard deviations obtained from bootstrapping.

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- ###### Figure 4

Experimental results on an expanding linear cluster state, where the leading qubit is measured in the Z basis after (a) one and (b) two interaction steps between the client and the server. (a) While the server observes mixed outcomes (squares, ∼2000 test and computation rounds each), for each α1, the client can decode the results using the secret keys. A fit to the decoded computation outcomes (circles) is shown to guide the eye. Error intervals indicate the binomial standard error. The test round errors are significantly below the threshold for verification of a two-node cluster state (dashed line). (b) The decoded outcome is shown for different blind measurement settings, (α1, α2), each comprising ∼3100 computation rounds (see Supplementary Material [ 32] for interleaved test round results).

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