Environmentally decoupled sds -wave Josephson junctions for quantum computing

• Published in: Nature (London) 1999-04, Vol.398 (6729), p.679-681
• Main Authors: Blatter, Gianni, Ioffe, Lev B, Geshkenbein, Vadim B, Feigel'man, Mikhail V, Fauchère, Alban L
• Format: Article
• Language: English
• Subjects: Computers; Humanities and Social Sciences; letter; multidisciplinary; Quantum theory; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/19464

Quantum computers have the potential to outperform their classical counterparts in a qualitative manner, as demonstrated by algorithms which exploit the parallelism inherent in the time evolution of a quantum state. In quantum computers, the information is stored in arrays of quantum two-level systems (qubits), proposals for which include utilizing trapped atoms and photons, magnetic moments in molecules and various solid-state implementations. But the physical realization of qubits is challenging because useful quantum computers must overcome two conflicting difficulties: the computer must be scalable and controllable, yet remain almost completely detached from the environment during operation, in order to maximize the phase coherence time. Here we report a concept for a solid-state 'quiet' qubit that can be efficiently decoupled from the environment. It is based on macroscopic quantum coherent states in a superconducting quantum interference loop. Our two-level system is naturally bistable, requiring no external bias: the two basis states are characterized by different macroscopic phase drops across a Josephson junction, which may be switched with minimal external contact.