Preparation of entangled W states with cat-state qubits in circuit QED
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Preparation of entangled W states with cat-state qubits in circuit QED Yu Zhang1 · Tong Liu2 · Yang Yu1 · Chui-Ping Yang2,3 Received: 3 January 2020 / Accepted: 1 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Cat-state qubits (qubits encoded with cat states) have recently attracted much attention because of their enhanced lifetimes with quantum error correction. We here consider a circuit QED system consisting of three superconducting qutrits, each coupled to an individual cavity but all coupled to a common cavity. We show that entangled W states of three cat-state qubits hosted by the three individual cavities can be prepared with only a few basic operations. The higher energy level of the qutrits is not occupied; thus, decoherence from this level of the qutrits is greatly suppressed. In addition, the W states can be prepared deterministically. Numerical simulations show that highfidelity production of the W states of three cat-state qubits is feasible with current circuit QED technology. This proposal is quite general and can be applied to create the proposed W states, with each cavity being a microwave or optical cavity and each qutrit being a three-level natural or artificial atom. Keywords Cat-state qubit · Cqubit · W entangled state · Circuit QED
1 Introduction Entanglement is of fundamental interest in testing quantum mechanics against local hidden theory [1,2], but also has practical applications in quantum communication and quantum information processing (QIP). In the past decade, much efforts have been devoted to generation of entangled states. On the other hand, there is much work on the investigation of entangled states of multiple qubits (i.e., two-state or two-level quantum systems). There exist two types of important multi-qubit entan-
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Chui-Ping Yang [email protected]
1
School of Physics, Nanjing University, Nanjing 210093, China
2
Quantum Information Research Center, Shangrao Normal University, Shangrao 334001, Jiangxi, China
3
Department of Physics, Hangzhou Normal University, Hangzhou 311121, China 0123456789().: V,-vol
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gled state. One is Greenberger–Horne–Zeilinger (GHZ) states [2], taking the form of √1 |00 . . . 0 + eiϕ |11 . . . 1 . The other is W states [3], which are expressed as 2 √1 Pz |0⊗(n−1) |1 for n qubits. Here, Pz is the symmetry permutation operator for n the qubits (1, 2, . . . , n), and Pz |0⊗(n−1) |1 denotes the totally symmetric state in which (n − 1) qubits out of a total of n qubits are in the state |0, while the remaining qubit is in the state |1. As an example, consider a three-qubit case (i.e., n = 3), for which the W state is √1 (|001 + |010 + |100) . It is known that the GHZ states 3 and the W states cannot be converted to each other by local operations and classical communications [3]. In the case of three qubits, it was shown [3] that tracing out a single qubit from a GHZ state results in a maximally mixed state while there is some genuine entanglement be
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