Abstract
Among the various approaches to quantum computing, all-optical architectures are especially promising due to the robustness and mobility of single photons. However, the creation of the two-photon quantum logic gates required for universal quantum computing remains a challenge. Here we propose a universal two-qubit quantum logic gate, where qubits are encoded in surface plasmons in graphene nanostructures, that exploits graphene's strong third-order nonlinearity and long plasmon lifetimes to enable single-photon-level interactions. In particular, we utilize strong two-plasmon absorption in graphene nanoribbons, which can greatly exceed single-plasmon absorption to create a “square-root-of-swap” that is protected by the quantum Zeno effect against evolution into undesired failure modes. Our gate does not require any cryogenic or vacuum technology, has a footprint of a few hundred nanometers, and reaches fidelities and success rates well above the fault-tolerance threshold, suggesting that graphene plasmonics offers a route towards scalable quantum technologies.
Highlights
Quantum computing could efficiently solve many essential problems
Driven by the Zeno effect, the strong nonlinearity of the graphene waveguides reduces the probability that two plasmons are found in the same nanoribbon and increases the success probability. c We describe the SWAP1/2 gate as a six-state system where U is the coupling between ribbons, while γ and γ(2) are the intrinsic damping and two-plasmon absorption rates, respectively state of the qubit
As a physical realization of such a graphene-based quantum gate, we envision a system of two graphene nanoribbons that support npj Quantum Information (2019) 37
Summary
Quantum computing could efficiently solve many essential problems. building a quantum computer is not an easy task. One promising approach is to use single-photons, whose weak interaction with the environment makes them perfectly suitable for encoding and transmitting quantum information This weak interaction strength makes the implementation of photon–photon interactions a significant challenge. (wherein continuous measurement prevents a quantum system from evolving), can boost the success probability of the gate to 100%.4 In this scenario, the quantum Zeno effect requires nonlinear two-photon absorption to occur at the singlephoton-level. The quantum Zeno effect requires nonlinear two-photon absorption to occur at the singlephoton-level To date, such a strong optical nonlinearity has only been achieved via complex interactions with atomic systems,[7] which lack scalability. In other words, |0〉 (|1〉) in the Fock basis represents a logical |0〉 (|1〉)
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