Abstract We propose a scheme for realizing multi-qubit entangled W-state and non-local CZ and C 2 Z gates via a cavity polariton blockade mechanism with a system of atomic qubits coupled to a common cavity mode. The polariton blockade is achieved by tuning the system, an N − qubit register, such that no two atoms are simultaneously excited to the qubit excited state, and there is an effective coupling only between the ground state and a singly-excited W state of the qubit register. The control step requires only an external drive of the cavity mode and a global qubit pulse and no individual qubit addressing. We analytically obtain the state preparation error upper bound for an N − qubit W state which scales as ( 1 − 1 / N ) / C where C is the single particle cooperativity. We additionally show the application of the polariton blockade mechanism in realizing a non-local CZ and C 2 Z gate by using a different set of computational qubit states, and characterize the gate infidelity upper bounds which scale as ∼ 1 / C .
Abstract We propose a scheme for realizing multi-qubit entangled W-state and non-local CZ and C 2 Z gates via a cavity polariton blockade mechanism with a system of atomic qubits coupled to a common cavity mode. The polariton blockade is achieved by tuning the system, an N − qubit register, such that no two atoms are simultaneously excited to the qubit excited state, and there is an effective coupling only between the ground state and a singly-excited W state of the qubit register. The control step requires only an external drive of the cavity mode and a global qubit pulse and no individual qubit addressing. We analytically obtain the state preparation error upper bound for an N − qubit W state which scales as ( 1 − 1 / N ) / C where C is the single particle cooperativity. We additionally show the application of the polariton blockade mechanism in realizing a non-local CZ and C 2 Z gate by using a different set of computational qubit states, and characterize the gate infidelity upper bounds which scale as ∼ 1 / C .
Manipulating the cavity-magnon polariton blockade is significant for achieving precise, on-demand control of individual photons (magnons) and has particular applications in realizing multifunctional quantum technologies, quantum information processing, and hybrid quantum networks. In this paper, we theoretically propose a scheme to realize an n-cavity-magnon polariton blockade in a cavity-magnon system by utilizing Kerr nonlinearity. We demonstrate that the Kerr nonlinearity introduces anharmonicity into the polariton energy spectrum, which in turn enables the blockade effect. When the external driving frequency is resonant with the transition to the nth polariton excited state, a perfect n-polariton blockade is achieved. Moreover, increasing the driving strength can enhance the higher-order blockade while maintaining high fidelity in a dissipative environment. Our work pioneers the field of cavity-magnon polariton blockade, opens a new avenue for the preparation of controllable quantum resources, and holds significant potential for applications in quantum communication and quantum information processing.
A neutral-atom system serves as a promising platform for realizing gate-based quantum computing because of its capability to trap and control several atomic qubits in different geometries and the ability to perform strong, long-range interactions between qubits; however, the two-qubit entangling gate fidelity lags behind competing platforms such as superconducting systems and trapped ions. The aim of our work is to design a fast, robust, high-fidelity controlled-Z (cz) gate, based on the Rydberg-blockade mechanism, for neutral atoms. We propose a gate procedure that relies on simultaneous and transitionless quantum driving of a pair of atoms using broadband lasers. By simulating a system of two interacting cesium atoms, including spontaneous emission from excited levels and parameter fluctuations, we yield a Rydberg-blockade cz gate with fidelity 0.9985 over an operation time of $0.12\phantom{\rule{3.33333pt}{0ex}}\mathrm{\textmu{}s}$. Our gate procedure delivers cz gates that are superior than the state-of-the-art experimental cz gate and the simulated cz gates based on adiabatic driving of atoms. Our results show that our gate procedure carries significant potential for achieving scalable quantum computing using neutral atoms.
We present two protocols for realizing deterministic nonlocal multiqubit quantum gates on qubits coupled to a common cavity mode. The protocols rely only on a classical drive of the cavity mode, while no external drive of the qubits is required. Applied to just two qubits, both protocols provide a universal gate set for quantum computing, together with single-qubit gates. In the first protocol, the state of the cavity follows a closed trajectory in phase space and accumulates a geometric phase depending on the state of the qubits. This geometric phase gate can be used together with global single-qubit gates to generate high-fidelity Greenberger--Horne--Zeilinger (GHZ) states. The second protocol uses an adiabatic evolution of the combined qubit-cavity system to accumulate a dynamical phase. Repeated applications of this protocol allow for the realization of a family of phase gates with arbitrary phases, e.g., phase-rotation gates and multi-controlled-Z gates. For both protocols, we provide analytic solutions for the error rates, which scale as $\ensuremath{\sim}N/\sqrt{C}$ in the presence of relevant losses, with C the cooperativity and N the qubit number. Our protocols are applicable to a variety of systems and can be generalized by replacing the cavity by a different bosonic mode, such as a phononic mode. We provide estimates of gate fidelities and durations for atomic and molecular qubits as well as superconducting fluxonium qubits coupled to optical or microwave cavities, and we outline implications for quantum error correction.
We propose an all optical quantum computation scheme, with trapped electron spin qubits, using their Coulomb exchange interaction with optically excited microcavity exciton-polaritons. This paper describes a single qubit rotation, which together with two-qubit controlled-z gate presented in PRB 85, 241403(R) (2012), form a set of universal logic gates. The errors due to finite cavity lifetime and incorrect orientation of the rotation axis are minimized by optimizing pump pulse parameters. With projective homodyne phase measurement and initialization, our scheme is a promising candidate for the physical realization of a universal quantum computer.
Cavity QED, wherein a quantum emitter is coupled to electromagnetic cavity modes, is a powerful platform for implementing quantum sensors, memories, and networks. However, due to the fundamental trade-off between gate fidelity and execution time, as well as limited scalability, the use of cavity QED for quantum computation was overtaken by other architectures. Here, we introduce a new element into cavity QED—a free charged particle, acting as a flying qubit. Using free electrons as a specific example, we demonstrate that our approach enables ultrafast, deterministic, and universal discrete-variable quantum computation in a cavity-QED-based architecture, with potentially improved scalability. Our proposal hinges on a novel excitation blockade mechanism in a resonant interaction between a free-electron and a cavity polariton. This nonlinear interaction is faster by several orders of magnitude with respect to current photon-based cavity-QED gates, enjoys wide tunability and can demonstrate fidelities close to unity. Furthermore, our scheme is ubiquitous to any cavity nonlinearity, either due to light-matter coupling as in the Jaynes-Cummings model or due to photon-photon interactions as in a Kerr-type many-body system. In addition to promising advancements in cavity-QED quantum computation, our approach paves the way towards ultrafast and deterministic generation of highly entangled photonic graph states and is applicable to other quantum technologies involving cavity QED. Published by the American Physical Society 2024
We propose a one-step scheme to implement a multiqubit controlled phase gate with one qubit simultaneously controlling multiple qubits with three-level atoms at distant nodes in coupled cavity arrays. Selective qubit-qubit couplings are achieved by adiabatically eliminating the atomic excited states and photonic states, and the required phase shifts between the control qubit and any target qubit can be realized through suitable choices of the parameters of the external fields. Moreover, the effective model is robust against decoherence because neither the atoms nor the field modes are excited during the gate operation, leading to a useful step toward scalable quantum computing networks.