Single-step implementation of a hybrid controlled-not gate with one superconducting qubit simultaneously controlling multiple target cat-state qubits

Abstract

Hybrid quantum gates have recently drawn considerable attention. They play significant roles in connecting quantum information processors with qubits of different encoding and have important applications in the transmission of quantum states between a quantum processor and a quantum memory. In this work, we propose a single-step implementation of a multi-target-qubit controlled-NOT gate with one superconducting (SC) qubit simultaneously controlling n target cat-state qubits. In this proposal, the gate is implemented with n microwave cavities coupled to a three-level SC qutrit. The two logic states of the control SC qubit are represented by the two lowest levels of the qutrit, while the two logic states of each target cat-state qubit are represented by two quasi-orthogonal cat states of a microwave cavity. This proposal operates essentially through the dispersive coupling of each cavity with the qutrit. The gate realization is quite simple because it requires only a single-step operation. There is no need of applying a classical pulse or performing a measurement. The gate operation time is independent of the number of target qubits, thus it does not increase as the number of target qubits increases. Moreover, because the third higher energy level of the qutrit is not occupied during the gate operation, decoherence from the qutrit is greatly suppressed. As an application of this hybrid multi-target-qubit gate, we further discuss the generation of a hybrid Greenberger-Horne-Zeilinger (GHZ) entangled state of SC qubits and cat-state qubits. As an example, we numerically analyze the experimental feasibility of generating a hybrid GHZ state of one SC qubit and three cat-state qubits within present circuit QED technology. This proposal is quite general and can be extended to implement a hybrid controlled-NOT gate with one matter qubit (of different type) simultaneously controlling multiple target cat-state qubits in a wide range of physical systems, such as multiple microwave or optical cavities coupled to a three-level natural or artificial atom.

Dissipative preparation and stabilization of many-body quantum states in a superconducting qutrit array

“…In the context of multiple qubits, this regime has been used to demonstrate a coherent entangling gate between non-interacting qubits [48,49]. In addition, the strong dispersive regime enables control and entanglement of quantum states encoded in cavity modes [50][51][52]. In this proposal, we will harness the strong dispersive regime to create autonomous feedback on the quantum state of two nearest-neighbor qutrits, the basic idea of which is introduced below with a comparatively simpler model of nearest-neighbor qubits.…”

Even and Odd Cat States of Two and Three Qubits in the Probability Representation of Quantum Mechanics

“…We also discuss the probability representation of even and odd cat states of an oscillating spin-1/2 particle. Our motivation to discuss these states is that the even and odd cat states of different oscillator systems, known as Schrödinger cat states [ 43 , 44 , 45 ], can be produced in various experiments [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ], and they can have several applications in quantum information processing schemes e.g., in optical quantum computation [ 55 , 56 , 57 , 58 ] and quantum communication [ 59 , 60 ]. The development of schemes for the generation and application of the considered cat states of oscillating spin-1/2 particles can be anticipated.…”