Observation of Energy Levels Quantization in Underdamped Josephson Junctions above the Classical-Quantum Regime Crossover Temperature

Silvestrini, P.; Palmieri, V.G.; Ruggiero, B.; Russo, M.

doi:10.1103/physrevlett.79.3046

Cited by 113 publications

(96 citation statements)

References 17 publications

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“…Some features of macroscopic quantum behavior were demonstrated such as 'macroscopic quantum tunneling' (MQT) of the flux, resonant tunneling and level quantization (Voss & Webb 1981, Martinis et al 1987, Clarke et al 1988, Rouse et al 1995, Silvestrini et al 1997. However, only very recently coherent superpositions of macroscopically different flux states have been demonstrated (Friedman et al 2000, van der Wal et al 2000.…”

Section: A Josephson Flux (Persistent Current) Qubitsmentioning

confidence: 99%

Quantum-state engineering with Josephson-junction devices

2001

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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 this purpose a number of individual two-state quantum systems (qubits) should be addressed and coupled in a controlled way. Several physical realizations of qubits have been considered, incl. trapped ions, NMR, and quantum optical systems. For potential applications such as logic operations, nano-electronic devices appear particularly promising because they can be embedded in electronic circuits and scaled up to large numbers of qubits.Here we review the quantum properties of low-capacitance Josephson junction devices. The relevant quantum degrees of freedom are either Cooper pair charges on small islands or fluxes in ring geometries, both in the vicinity of degeneracy points. The coherence of the superconducting state is exploited to achieve long phase coherence times. Single-and two-qubit quantum manipulations can be controlled by gate voltages or magnetic fields, by methods established for single-charge systems or the SQUID technology. Several of the interesting single-qubit properties, incl. coherent oscillations have been demonstrated in recent experiments, thus displaying in a spectacular way the laws of quantum mechanics in solid state devices. Further experiments, such as entanglement of qubit states, which are crucial steps towards a realization of logic elements, should be within reach.In addition to the manipulation of qubits the resulting quantum state has to be read out. For a Josephson charge qubit this can be accomplished by coupling it capacitively to a single-electron transistor (SET). To describe the quantum measurement process we analyze the time evolution of the density matrix of the coupled system. As long as the transport voltage is turned off, the transistor has only a weak influence on the qubit. When the voltage is switched on, the dissipative current through the SET destroys the phase coherence of the qubit within a short time. The measurement is accomplished only after a longer time, when the macroscopic signal, i.e., the current through the SET, resolves different quantum states. At still longer times the measurement process itself destroys the information about the initial state. Similar scenarios are found when the quantum state of a flux qubit is measured by a dc-SQUID, coupled to it inductively.

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Section: A Josephson Flux (Persistent Current) Qubitsmentioning

confidence: 99%

Quantum-state engineering with Josephson-junction devices

2001

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“…By applying a resonant time-dependent external rf-field, Han et al [31] created a population inversion between the two adjacent fluxoid wells. Furthermore, Silvestrini et al [32] reported the observation of energy level quantization in underdamped Josephson junctions above the crossover temperature which separates the classical from the quantum regime. Han et al [33] recently presented evidence for transitions between the fluxoid wells due to cascaded, two-photon processes.…”

Section: A Experimentsmentioning

confidence: 99%

“…A second class of experiments addresses tunneling of the magnetic flux in superconducting quantum interference devices (SQUIDs) [28][29][30][31][32][33][34][35][36]. The dynamics of the total flux threaded through the SQUID (or the phase difference across a current biased Josephson junction) obeys a collective motion of a macroscopic number of quasiparticles.…”

Section: A Experimentsmentioning

confidence: 99%

Strong Coupling Theory for Tunneling and Vibrational Relaxation in Driven Bistable Systems

2001

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A study of the dynamics of a tunneling particle in a driven bistable potential which is moderatelyto-strongly coupled to a bath is presented. Upon restricting the system dynamics to the Hilbert space spanned by the M lowest energy eigenstates of the bare static potential, a set of coupled non-Markovian master equations for the diagonal elements of the reduced density matrix, within the discrete variale representation, is derived. The resulting dynamics is in good agreement with predictions of ab-initio real-time path integral simulations. Numerous results, analytical as well as numerical, for the quantum relaxation rate and for the asymptotic populations are presented. Our method is particularly convenient to investigate the case of shallow, time-dependent potential barriers and moderate-to-strong damping, where both a semi-classical and a Redfield-type approach are inappropriate.PACS: 82.20.Pm

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“…This typically leads to features on the distributions which are more narrow than σ I . In such cases 12,16 we have taken the width of these smaller features. If data of multiple samples were discussed in a reference, the data of the sample with the smallest relative P (I) width is considered.…”

Section: Experimental Resolutionmentioning

confidence: 99%

“…At low temperatures the quantum mechanical properties of Josephson junctions have been investigated in relation to macroscopic quantum tunneling (MQT) 13,14,15 , energy level quantization (ELQ) 12,16 and macroscopic quantum coherence (MQC) 17 . Recently, the quantum mechanical properties of Josephson junction systems have regained interest in the view of their possible application for solid state based quantum information processing 18,19,20 .…”

Section: Introductionmentioning

confidence: 99%

Switching current measurements of large area Josephson tunnel junctions

Wallraff

Lukashenko

Coqui

et al. 2003

Review of Scientific Instruments

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We have developed a scheme for a high resolution measurement of the switching current distribution of a current biased Josephson tunnel junction using a timing technique. The measurement setup is implemented such that the digital control and read-out electronics are optically decoupled from the analog bias electronics attached to the sample. We have successfully used this technique to measure the thermal activation and the macroscopic quantum tunneling of the phase in a small Josephson tunnel junction with a high experimental resolution. This technique may be employed to characterize current-biased Josephson tunnel junctions for applications in quantum information processing.

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Observation of Energy Levels Quantization in Underdamped Josephson Junctions above the Classical-Quantum Regime Crossover Temperature

Cited by 113 publications

References 17 publications

Quantum-state engineering with Josephson-junction devices

Quantum-state engineering with Josephson-junction devices

Strong Coupling Theory for Tunneling and Vibrational Relaxation in Driven Bistable Systems

Switching current measurements of large area Josephson tunnel junctions

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