A Multi-Qubit Quantum Gate Using the Zeno Effect

Journal Article · Thu Sep 07 00:00:00 EDT 2023 · Quantum

DOI:https://doi.org/10.22331/q-2023-09-07-1100· OSTI ID:1998804

Lewalle, Philippe ^[1]; Martin, Leigh S. ^[2]; Flurin, Emmanuel ^[2]; Zhang, Song ^[3]; Blumenthal, Eliya ^[4]; Hacohen-Gourgy, Shay ^[4]; Burgarth, Daniel ^[5]; Whaley, K. Birgitta ^[1]

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1. Berkeley Center for Quantum Information and Computation, Berkeley, California 94720 USA, Department of Chemistry, University of California, Berkeley, California 94720 USA
2. Berkeley Center for Quantum Information and Computation, Berkeley, California 94720 USA, Department of Physics, University of California, Berkeley, California 94720 USA
3. Department of Chemistry, University of California, Berkeley, California 94720 USA
4. Department of Physics, Technion - Israel Institute of Technology, Haifa 32000 Israel
5. Center for Engineered Quantum Systems, Macquarie University, 2109 NSW, Australia

The Zeno effect, in which repeated observation freezes the dynamics of a quantum system, stands as an iconic oddity of quantum mechanics. When a measurement is unable to distinguish between states in a subspace, the dynamics within that subspace can be profoundly altered, leading to non-trivial behavior. Here we show that such a measurement can turn a non-interacting system with only single-qubit control into a two- or multi-qubit entangling gate, which we call a Zeno gate. The gate works by imparting a geometric phase on the system, conditioned on it lying within a particular nonlocal subspace. We derive simple closed-form expressions for the gate fidelity under a number of non-idealities and show that the gate is viable for implementation in circuit and cavity QED systems. More specifically, we illustrate the functioning of the gate via dispersive readout in both the Markovian and non-Markovian readout regimes, and derive conditions for longitudinal readout to ideally realize the gate.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-05CH11231; 2020166; 1106400
• OSTI ID: 1998804
• Journal Information: Quantum, Journal Name: Quantum Vol. 7; ISSN 2521-327X
• Publisher: Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften
• Country of Publication: Austria
• Language: English