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Low-capacitance Josephson junction arrays in the parameter range where single charges can be controlled are suggested as possible physical realiza-tions of the elements which have been considered in the context of quantum computers. We discuss single and multiple quantum bit systems. The systems are controlled by applied gate voltages, which also allow the… (More)

- Alexander Shnirman, Gerd Schön, Ivar Martin, Yuriy Makhlin
- Physical review letters
- 2005

Recent experiments indicate a connection between the low- and high-frequency noises affecting superconducting quantum systems. We explore the possibilities that both noises can be produced by one ensemble of microscopic modes, made up, e.g., by sufficiently coherent two-level systems (TLS's). This implies a relation between the noise power in different… (More)

- I Martin, L Bulaevskii, A Shnirman
- Physical review letters
- 2005

We consider a two-level system (TLS) with energy level separation plankvOmega0 inside a Josephson junction. The junction is shunted by a resistor R and is voltage V biased. If the TLS modulates the Josephson energy and/or is optically active, it is Rabi driven by the Josephson oscillations in the running phase regime near the resonance 2eV=plankvOmega0. The… (More)

- J P Pekola, V Brosco, M Möttönen, P Solinas, A Shnirman
- Physical review letters
- 2010

One of the challenges of adiabatic control theory is the proper inclusion of the effects of dissipation. Here we study the adiabatic dynamics of an open two-level quantum system deriving a generalized master equation to consistently account for the combined action of the driving and dissipation. We demonstrate that in the zero-temperature limit the ground… (More)

- J Lisenfeld, C Müller, +4 authors A V Ustinov
- Physical review letters
- 2010

We demonstrate a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. It allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. We apply this method to measure the temperature dependence of TLS coherence for the first… (More)

Quantum state engineering, i.e., active control over the coherent dynamics of suitable quantum mechanical systems, has become a fascinating perspective of modern physics. With concepts developed in atomic and molecular physics and in the context of NMR, the field has been stimulated further by the perspectives of quantum computation and communication. For… (More)

- Julian Hauss, Arkady Fedorov, Carsten Hutter, Alexander Shnirman, Gerd Schön
- Physical review letters
- 2008

For a superconducting qubit driven to perform Rabi oscillations and coupled to a slow electromagnetic or nanomechanical oscillator we describe previously unexplored quantum optics effects. When the Rabi frequency is tuned to resonance with the oscillator, the latter can be driven far from equilibrium. Blue detuned driving leads to a population inversion in… (More)

Low-capacitance Josephson junctions, where Cooper pairs tunnel coherently while Coulomb blockade effects allow the control of the total charge, provide physical realizations of quantum bits (qubits), with logical states differing by one Cooper-pair charge on an island. The single-and two-bit operations required for quantum computation can be performed by… (More)

- Robert S Whitney, Yuriy Makhlin, Alexander Shnirman, Yuval Gefen
- Physical review letters
- 2005

We investigate the geometric phase or Berry phase acquired by a spin half which is both subject to a slowly varying magnetic field and weakly coupled to a dissipative environment (either quantum or classical). We study how this phase is modified by the environment and find that the modification is of a geometric nature. While the original Berry phase (for… (More)

Motivated by recent experiments with Josephson-junction circuits we reconsider de-coherence effects in quantum two-level systems (TLS). On one hand, the experiments demonstrate the importance of 1/f noise, on the other hand, by operating at symmetry points one can suppress noise effects in linear order. We, therefore, analyze noise sources with a variety of… (More)