Multiqubit tunable phase gate of one qubit simultaneously controllingnqubits in a cavity

Abstract

We propose how to realize a multiqubit tunable phase gate of one qubit simultaneously controlling n qubits with four-level quantum systems in a cavity or coupled to a resonator. Each of the n twoqubit controlled-phase (CP) gates involved in this multiqubit phase gate has a shared control qubit but a different target qubit. In this propose, the two lowest levels of each system represent the two logical states of a qubit while the two higher-energy intermediate levels are used for the gate implementation. The method presented here operates essentially by creating a single photon through the control qubit, which then induces a phase shift to the state of each target qubit. The phase shifts on each target qubit can be adjusted by changing the Rabi frequencies of the pulses applied to the target qubit systems. The operation time for the gate implementation is independent of the number of qubits, and neither adjustment of the qubit level spacings nor adjustment of the cavity mode frequency during the gate operation is required by this proposal. It is also noted that this approach can be applied to implement certain types of significant multiqubit phase gates, e.g., the multiqubit phase gate consisting of n two-qubit CP gates which are key elements in quantum Fourier transforms. A possible physical implementation of our approach is presented. Our proposal is quite general, and can be applied to physical systems such as various types of superconducting devices coupled to a resonator and trapped atoms in a cavity.

One-step implementation of a multiqubit controlled-phase gate with superconducting quantum interference devices coupled to a resonator

“…Accordingly, δ j and Ω j are considered to be different for different qubits. Under the conditions ofΔ j ≫ g j and Δ j ≫ Ω j , the effective Hamiltonian for n SQUIDs coupled to a single-mode resonator and the microwave pulses in the interaction picture is [15,32,34]…”

“…Recently, some schemes for generating multiqubit quantum gates have been proposed with several operational steps, which largely simplify the operation complexity compared with the protocols based on the gate-composition method. For example, Yang et al proposed a series of multiqubit controlled-logic gates in a SQUID system, ranging from n-qubit control of one target qubit [29,30] to one-qubit control of n target qubits [31,32]. These schemes are important because they open new avenues for creating SQUID-based quantum computation.…”

Circuit QED: single-step realization of a multiqubit controlled phase gate with one microwave photonic qubit simultaneously controlling n − 1 microwave photonic qubits

“…How to efficiently implement this multiqubit gate becomes necessary and important. Over the past years, based on cavity QED or circuit QED, many efficient methods have been proposed for the direct implementation of this multiqubit phase gate, by using natural atoms or artificial atoms (e.g., superconducting qubits, quantum dots, or nitrogen-vacancy center ensembles) [19][20][21][22][23].…”

Entanglement generation and quantum information transfer between spatially-separated qubits in different cavities

“…Also, the experimental creation of a Fock state and a superposition of Fock states of a single superconducting cavity using a superconducting qubit have been reported [23,24]. Moreover, a large number of theoretical proposals have been presented for realizing quantum information transfer, logical gates and entanglement with two or more superconducting qubits embedded in a cavity or coupled by a resonator [25][26][27][28][29][30][31][32][33][34]. Hereafter, we use the terms cavity and resonator interchangeably.…”