Multiplex-controlled phase gate with qubits distributed in a multicavity system

Abstract

We present a way to realize a multiplex-controlled phase gate of n−1 control qubits simultaneously controlling one target qubit, with n qubits distributed in n different cavities. This multiqubit gate is implemented by using n qutrits ( three-level natural or artificial atoms) placed in n different cavities, which are coupled to an auxiliary qutrit. Here, the two logic states of a qubit are represented by the two lowest levels of a qutrit placed in a cavity. We show that this n-qubit controlled phase gate can be realized using only 2n + 2 basic operations, i.e., the number of required basic operations only increases linearly with the number n of qubits. Since each basic operation employs the qutrit-cavity or qutrit-pulse resonant interaction, the gate can be fast implemented when the number of qubits is not large. Numerical simulations show that a three-qubit controlled phase gate, which is executed on three qubits distributed in three different cavities, can be high-fidelity implemented by using a circuit QED system. This proposal is quite general and can be applied to a wide range of physical systems, with atoms, NV centers, quantum dots, or various superconducting qutrits distributed in different cavities. Finally, this method can be applied to implement a multiqubit controlled phase gate with atoms using a cavity. A detailed discussion on implementing a three-qubit controlled phase gate with atoms and one cavity is presented.

Transferring entangled states of photonic cat-state qubits in circuit QED

“…The result (21) was derived under the conditions (5), (6), (18) and (19) given above. The conditions (5) and (18) can be satisfied by choosing g 1 = g 2 and g 3 = g 4 .…”

“…The fidelity of the entangled state transfer is given by F = ψ id | ρ |ψ id , where |ψ id is the ideal output state of the four cavities given in Eq. (21), while ρ is the reduced density operator of the four cavities after tracing ρ over the degrees of the coupler qutrit, when the state transfer is carried out in a realistic system (with dissipation and dephasing considered).…”

Implementing a multi-target-qubit controlled-not gate with logical qubits outside a decoherence-free subspace and its application in creating quantum entangled states

“…The direct realization of a Toffoli gate of three physical qubits has been experimentally demonstrated in various physical systems [11][12][13]. In addition, based on cavity or circuit QED, many schemes have been presented for the direct realization of a multi-control-qubit gate [14][15][16][17][18][19][20][21][22] and a multi-target-qubit gate [23][24][25][26][27][28][29] with physical qubits.…”

“…Because the two logic states |0 and |1 of a physical qubit do not form a DFS, the states of the physical qubits do not stay in a DFS for all three stages: (i) before the gate operation, (ii) during the gate operation, and (iii) after the gate operation. In this sense, by using the previous proposals [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], quantum states of qubits will undergo decoherence from all of these three stages. Also, because the states of physical qubits do not stay in a DFS, the errors caused by decoherence from each of the three stages accumulate for a long-running 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

“…Hence, it is worthwhile to seek efficient approaches to realize multiqubit quantum gates. Many efficient schemes have been presented for the direct realization of a multiqubit controlled-phase or controlled-NOT gate, with multiple-control qubits acting on one target qubit [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. This type of multiqubit gate is of significance in QIP, such as quantum algorithms and error corrections.…”