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Optics Express

Tunable superradiance and quantum phase gate based on graphene wrapped nanowire

Weixuan Zhang, Junfeng Ren, Xiangdong Zhang

Published Aug 17, 2015• 10 citations
Publisher

Abstract

The interaction between quantum emitters and graphene wrapped nanowire has been investigated using a Green's function technique. The eigenmodes for the graphene wrapped nanowire at various Fermi levels in graphene have been solved exactly. The Dicke subradiance and superradiance resulting from the graphene-mediated interaction have been observed. Based on these phenomena, we have proposed a scheme for a deterministic tunable two-qubit quantum phase gate. The "switching" effect for the quantum phase gate has been realized theoretically by changing an external voltage, which is very beneficial for the quantum-information processing.

DOI
10.1364/oe.23.022347

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The interaction between quantum emitters and graphene wrapped nanowire has been investigated using a Green's function technique. The eigenmodes for the graphene wrapped nanowire at various Fermi levels in graphene have been solved exactly. The Dicke subradiance and superradiance resulting from the graphene-mediated interaction have been observed. Based on these phenomena, we have proposed a scheme for a deterministic tunable two-qubit quantum phase gate. The "switching" effect for the quantum phase gate has been realized theoretically by changing an external voltage, which is very beneficial for the quantum-information processing.
A graphene wrapped dielectric particle has been proposed theoretically to realize tunable multi-qubit quantum phase gates (QPGs) with ultrahigh fidelity. By using a first-principles Green’s function technique, the interactions between quantum emitters mediated by graphene plasmons have been investigated. We find that the spontaneous decay rates of these emitters can be strongly enhanced and controlled by means of the efficient excitations of eigenmodes in graphene. The collective subradiance and superradiance resulting from the graphene-mediated interactions have been predicted. Based on these phenomena, we propose the tunable multi-qubit QPGs. These phase gates have the advantage of sensitive adjustability by changing the Fermi level or the electrostatic gating in graphene, at the same time they possess very high fidelities due to the small dissipation in the graphene monolayer.
The Dicke subradiance and superradiance resulting from the interaction between surface plasmons of nanospheres and an ensemble of quantum emitters have been investigated by using a Green's function approach. Based on such an investigation, we propose a scheme for a deterministic multi-qubit quantum phase gate. The case of single sphere has been compared with nanosphere cluster which possesses hot spots. The potential application of present phenomena to the quantum-information processing is anticipated.
The Dicke subradiance and superradiance resulting from the interaction between surface plasmons of a nanosphere and an ensemble of quantum emitters have been investigated using a Green’s function approach. Based on such an investigation, we propose a scheme for a deterministic multi-qubit quantum phase gate. As an example, two-qubit, three-qubit, and four-qubit quantum phase gates have been designed and analyzed in detail. Phenomena due to the losses in the metal are discussed. Potential applications of these phenomena to quantum-information processing are anticipated.
We investigate a system consisting of a single, as well as two emitters strongly coupled to surface plasmon modes of a nanowire using a Green's function approach. Explicit expressions are derived for the spontaneous decay rate into the plasmon modes and for the atom-plasmon coupling as well as a plasmon-mediated atom-atom coupling. Phenomena due to the presence of losses in the metal are discussed. In case of two atoms, we observe Dicke subradiance and superradiance resulting from their plasmon-mediated interaction. Based on this phenomenon, we propose a scheme for a deterministic two-qubit quantum gate. We also discuss a possible realization of interesting many-body Hamiltonians, such as the spin-boson model, using strong emitter-plasmon coupling.
We propose to combine the advantages of graphene, such as easy tunability and long coherence times, with Josephson physics to manufacture qubits. If these qubits are built around a 0 and π\piπ junction they can be controlled by an external flux. Alternatively, a d-wave Josephson junction can itself be tuned via a gate voltage to create superpositions between macroscopically degenerate states. We show that ferromagnets are not required for realizing π\piπ junction in graphene, thus considerably simplifying its physical implementation. We demonstrate how one qubit gates, such as arbitrary phase rotations and the exchange gate, can be implemented.
Controlling the energy spectrum of quantum-coherent superconducting circuits, i.e., the energies of excited states, the circuit anharmonicity, and the states' charge dispersion, is essential for designing performant qubits. This control is usually achieved by adjusting the circuit's geometry. In situ control is traditionally obtained via an external magnetic field, in the case of tunnel Josephson junctions. More recently, semiconductor-weak-links-based Josephson junctions have emerged as an alternative building block with the advantage of tunability via the electric-field effect. Gate-tunable Josephson junctions have been succesfully integrated in superconducting circuits using, for instance, semiconducting nanowires or two-dimensional electron gases. In this Letter we demonstrate, in a graphene superconducting circuit, a large gate tunability of qubit properties: frequency, anharmonicity, and charge dispersion. We rationalize these features using a model considering the transmission of Cooper pairs through Andreev bound states. Noticeably, we show that the high transmission of Cooper pairs in such weak link strongly suppresses the charge dispersion. Our Letter illustrates the potential for graphene-based qubits as versatile building blocks in advanced quantum circuits.