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International Congress on Advanced Electromagnetic Materials in Microwaves and Optics

Multi-qubit quantum phase gates based on plasmonic nanospheres

Junfeng Ren, Xiaochen Zhang

Published Sep 1, 2016• 0 citations
Publisher

Abstract

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.

DOI
10.1109/metamaterials.2016.7746379

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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.
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.
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.
The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green's tensor technique. We have demonstrated that multi-qubit entanglements for two-level QEs can be produced at different coupling resonance frequencies, when they locate in the hot spots of the metallic nanoparticle cluster. The duration of quantum beats for such an entanglement can reach two orders longer than that for the entanglement in a photonic cavity. The phenomenon originates from collective coupling resonance excitation of the cluster. At the frequency of single scattering resonance, the entanglement cannot be produced although the single QE spontaneous decay rate is very big.
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.
Multiqubit entanglement is extremely important to perform truly secure quantum optical communication and computing operations. However, the efficient generation of long-range entanglement over extended time periods between multiple qubits randomly distributed in a photonic system remains an outstanding challenge. This constraint is mainly due to the detrimental effects of decoherence and dephasing. To alleviate this issue, we present engineered epsilon-near-zero (ENZ) nanostructures that can maximize the coherence of light–matter interactions at room temperature. We investigate a practical ENZ plasmonic waveguide system, which simultaneously achieves multiqubit entanglement in elongated distances, extended time periods, and, even more importantly, independent of the emitters' positions. More specifically, we present efficient transient entanglement between three and four optical qubits mediated by ENZ with results that can be easily generalized to an arbitrary number of emitters. The entanglement between multiple qubits is characterized by computing the negativity metric applied to the proposed nanophotonic ENZ configuration. The ENZ response is found to be substantially advantageous to boost the coherence between multiple emitters compared to alternative plasmonic waveguide schemes. Finally, the super-radiance collective emission response at the ENZ resonance is utilized to design a high fidelity two-qubit quantum phase gate that can be used in various emerging quantum computing applications.