The dielectric cylinder covered with graphene (DCCG) is found to be a promising platform for studying multi-qubit collective effects. The plasmons supported by DCCG have huge wave numbers and low loss. Under some conditions, the zeroth- and first-order modes even have the same wavelength. Qubits along DCCG can interact with each other strongly by coupling with the plasmons within tens to hundreds of plasmonic wavelengths. Additionally, the electro-optical tunability of graphene means that we can manipulate the plasmonic wavelength and subsequently the dynamic evolutions of the qubits mediated by the DCCG conveniently. These properties make the graphene be a potential choice for quantum information device.
The dielectric cylinder covered with graphene (DCCG) is found to be a promising platform for studying multi-qubit collective effects. The plasmons supported by DCCG have huge wave numbers and low loss. Under some conditions, the zeroth- and first-order modes even have the same wavelength. Qubits along DCCG can interact with each other strongly by coupling with the plasmons within tens to hundreds of plasmonic wavelengths. Additionally, the electro-optical tunability of graphene means that we can manipulate the plasmonic wavelength and subsequently the dynamic evolutions of the qubits mediated by the DCCG conveniently. These properties make the graphene be a potential choice for quantum information device.
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.
We investigate entanglement mediated by DC current induced nonreciprocal graphene plasmon polaritons. Nonreciprocal systems are ideal for the enhancement, control, and preservation of entanglement due to the potential for unidirectional beam-like wave propagation, i.e., efficiently transporting photons from one emitter to another. Using a quantum master equation and three-dimensional Green's function analysis, we investigate a system consisting of two two-level emitters dominantly interacting via electric current induced nonreciprocal plasmonic modes of a graphene waveguide. We use concurrence as a measure of entanglement. We show that nonreciprocal graphene plasmon polaritons are a promising candidate to generate and mediate concurrence, where it is shown that there is good enhancement and control of entanglement over vacuum, which is beneficial for the broad applications of entanglement as a quantum resource. We believe our findings contribute to the development of quantum devices, enabling efficient and tunable entanglement between two-level systems, which is a central goal in quantum technologies.
A scheme to construct analogical atoms using graphene nanostructures via quantum nonlinearity is proposed. Due to the strong field localization capability of graphene plasmons and the significant intrinsic nonlinearity of graphene, a strong nonlinear optical response can be realized even with single-photon excitation. In this process, the quantum vacuum localized plasmonic mode plays a crucial role in achieving the third-order multi-photon nonlinear effect. The eigenfrequency of the nanostructure can shift by an amount tens of times larger than the decay rate, causing the nanostructure cavity to exhibit atomic-like behaviors. Furthermore, multilevel atoms can be constructed through the interaction of composite graphene nanostructures. The parameters of these atoms can be manipulated by adjusting the nanostructure size, Fermi energy, and other parameters. This research holds significant potential for applications in highly integrated, controllable nanophotonics.
We propose a novel approach for microwave and optical fields entanglement using an electrical capacitor loaded with graphene plasmonic waveguide. In the proposed scheme, a quantum microwave signal of frequency ωmdrives the electrical capacitor, while an intensive optical field (optical pump) of frequency ω1is launched to the graphene waveguide as a surface plasmon polariton (i.e., SPP) mode. The two fields interact by the means of electrically modulating the graphene optical conductivity. It then follows that an upper and lower SPP sideband modes (of ω2= ω1+ ωmand ω3= ω1- ωmfrequencies, respectively) are generated. We show that the microwave signal and the lower sideband SPP mode are entangled, for a proper optical intensity. A quantum mechanics model is carried out to describe the fields evolution. Furthermore, novel iterative approach (based on combining the Duan criterion with the quantum regression theorem) is developed to assess the fields entanglement. Consequently, the entanglement of the two fields is evaluated versus several parameters including the waveguide length, the pump intensity, and the microwave frequency. We find that the two fields are entangled over a vast microwave frequency range. Moreover, our calculations show that a significant number of entangled photons are generated at the lower SPP sideband. The proposed scheme attains tunable mechanism for microwave-optical entanglement which paves the way for efficient quantum systems.
Inspired by the remarkable ability of plasmons to boost radiative emission rates, we propose leveraging acoustic graphene plasmons (AGPs) to realize tunable, giant Purcell enhancements for single-photon, entangled-photon, and multipolar quantum emitters. These AGPs are localized inside a cavity defined by a graphene sheet and a metallic nanocube and filled with a dielectric of thickness of a few nanometers and consisting of stacked layers of 2D materials, containing impurities or defects that act as quantum light emitters. Through finite-difference time domain (FDTD) calculations, we show that this geometry can achieve giant Purcell enhancement factors over a large portion of the infrared (IR) spectrum, up to 6 orders of magnitude in the mid-IR and up to 4 orders of magnitude at telecommunications wavelengths, reaching quantum efficiencies of 95\% and 89\%, respectively, with high-mobility graphene. We obtain Purcell enhancement factors for single-photon electric dipole (E1), electric quadrupole (E2), and electric octupole (E3) transitions and two-photon spontaneous emission (2PSE) transitions, of the orders of 104, 107, 109, and 109, respectively, and a quantum efficiency of 79\% for entangled-photon emission with high-mobility graphene at a wavelength of λ=1.55μm. Importantly, AGP mode frequencies depend on the graphene Fermi energy, which can be tuned via electrostatic gating to modulate fluorescence enhancement in real time. As an example, we consider the Purcell enhancement of spontaneous single- and two-photon emissions from an erbium atom inside single-layer (SL) WS2. Our results could be useful for electrically tunable quantum emitter devices with applications in quantum communication and quantum information processing.
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.