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Josephson-junction qubits

delete2000-09-01
delete15
PRE
AI
Y
Yuriy Makhlin *
G
Gerd Schön
A
Alexander Shnirman
DOI：10.1002/1521-3978(200009)48:9/11<1043::AID-PROP1043>3.0.CO;2-Fdelete
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Abstract

Abstract

En 中文
Among the potential physical implementations of quantum bits (qubits) solid state devices appear most promising for large scale applications and integration in electronic circuits. Devices based on low-capacitance Josephson junctions exploit the coherence of the superconducting state, combined with the possibility to control individual charges by Coulomb blockade effects. The logical states in these systems differ by one Cooper-pair charge. Single- and two-bit operations can be performed by applying a sequence of gate voltages. The phase coherence rime is sufficiently long to allow a series of these steps. If, in addition, the strength of the Josephson coupling is controlled (e.g. by currents in SQUID loops) the system is ideal for quantum computation. Recent experiments by Nakamura et al. show the feasibility of this approach. In addition to the manipulations of qubits the resulting quantum state has to be read out. This quantum measurement process can be accomplished by coupling a single-electron transistor (SET) capacitively to the qubit. We investigate the process by analyzing the time-evolution of the density matrix of the coupled system. The measurement process is characterized by three time scales: the dephasing time, which is fast when a dissipative current flows in the SET, a longer 'measurement time' needed to read out the signal, and a third, even longer 'mixing time', characterizing measurement induced transitions which destroy the information about the initial quantum state. The noise spectrum of the current in the SET displays these time scales and allows their direct observation.
Keywords:
MACROSCOPIC QUANTUM STATES
SINGLE-ELECTRON
SYSTEM
COMPUTATION
DETECTOR
DYNAMICS
DOT
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Journal

F
Fortschritte der Physik-Progress of Physics
IF:
7.8
Papers:
2.0K
Citations:
3.6K

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