Quantum oscillations in two coupled charge qubits

Abstract

A practical quantum computer, if built, would consist of a set of coupled two-level quantum systems (qubits). Among the variety of qubits implemented, solid-state qubits are of particular interest because of their potential suitability for integrated devices. A variety of qubits based on Josephson junctions have been implemented; these exploit the coherence of Cooper-pair tunnelling in the superconducting state. Despite apparent progress in the implementation of individual solid-state qubits, there have been no experimental reports of multiple qubit gates--a basic requirement for building a real quantum computer. Here we demonstrate a Josephson circuit consisting of two coupled charge qubits. Using a pulse technique, we coherently mix quantum states and observe quantum oscillations, the spectrum of which reflects interaction between the qubits. Our results demonstrate the feasibility of coupling multiple solid-state qubits, and indicate the existence of entangled two-qubit states.

Preparation and manipulation of a fault-tolerant superconducting qubit

“…We show that their physical properties simplify the implementation of the difficult steps mentioned above. In these systems one may use the charge 14,15,16 or the conjugate phase degree of freedom 17,18 to store and process quantum information. Typically, one adjusts the parameters such that the ground state is (almost) doubly degenerate, and at low energies the system reduces to a qubit.…”

Dynamics of coupled spins in the white- and quantum-noise regime

“…In view of the substantial progress in fabrication of coupled qubit devices [3,4] and major advances in quantum state manipulation towards quantum computation [5], there is growing interest in the accurate calculation of the dynamics of coupled spins for realistic environmental couplings.…”

Josephson charge qubits: a brief review

“…Superconducting qubits utilize charge [5][6][7] or flux [8] degrees of freedom, or energy levels quantization in a single current-biased Josephson junction [9,10]. Inter-qubit coupling [15][16][17][18][19][20] and also quantum logic gates [21][22][23] have been reported later. Further progress in the field slowed down due to obvious decoherence issues that are still to be overcome in order to implement a working quantum computer.…”