Showing papers by "Robert Schoelkopf published in 2005"
TL;DR: In a Rabi oscillation experiment with a superconducting qubit, it is shown that a visibility in the qubit excited state population of more than 95% can be attained.
Abstract: In a Rabi oscillation experiment with a superconducting qubit we show that a visibility in the qubit excited state population of more than 95% can be attained We perform a dispersive measurement of the qubit state by coupling the qubit non-resonantly to a transmission line resonator and probing the resonator transmission spectrum The measurement process is well characterized and quantitatively understood In a measurement of Ramsey fringes, the qubit coherence time is larger than 500 ns
531 citations
TL;DR: Spectroscopy of a superconducting charge qubit coupled nonresonantly to a single mode of an on-chip resonator and a crossover in line shape with measurement power is observed and theoretically explained.
Abstract: We have recently demonstrated that a superconducting quantum two-level system can be strongly coupled to a single microwave photon [1] The strong coupling between a quantum solid state circuit and an individual photon, analogous to atomic cavity quantum electrodynamics (CQED) [2], has previously been envisaged by many authors, see Ref 3 and references therein Our circuit quantum electrodynamics architecture [3], in which a superconducting charge qubit, the Cooper pair box [4], is coupled strongly to a coplanar transmission line resonator, has great prospects both for performing quantum optics experiments [5] in solids and for realizing elements for quantum information processing [6] with superconducting circuits [7] In this letter we present spectroscopic measurements which demonstrate the non-resonant (dispersive) strong coupling between a Cooper pair box and a coherent microwave field in a high quality cavity The quantum state of the Cooper pair box is controlled using resonant microwave radiation and is read out with a dispersive quantum non-demolition (QND) measurement [3, 8, 9] The interaction between the Cooper pair box and the measurement field containing n photons on average gives rise to a large ac-Stark shift of the qubit energy levels, analogous to the one observed in CQED [10] As a consequence of the strong coupling, quantum fluctuations in n induce a broadening of the transition line width, characterizing the back action of the measurement on the qubit
439 citations
TL;DR: In this article, the authors presented fabrication and characterization procedures of devices for circuit quantum electrodynamics (cQED) with 3-GHz cavities with quality factors in the range 10/sup 4/-10/10/sup 6/, which allow access to the strong coupling regime of cQED.
Abstract: We present fabrication and characterization procedures of devices for circuit quantum electrodynamics (cQED). We have made 3-GHz cavities with quality factors in the range 10/sup 4/-10/sup 6/, which allow access to the strong coupling regime of cQED. The cavities are transmission line resonators made by photolithography. They are coupled to the input and output ports via gap capacitors. An Al-based Cooper pair box is made by e-beam lithography and Dolan bridge double-angle evaporation in superconducting resonators with high quality factor. An important issue is to characterize the quality factor of the resonators. We present an RF-characterization of superconducting resonators as a function of temperature and magnetic field. We have realized different versions of the system with different box-cavity couplings by using different dielectrics and by changing the box geometry. Moreover, the cQED approach can be used as a diagnostic tool of qubit internal losses.
209 citations
TL;DR: A novel phase-sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and the nonlinear regime, and observes for the first time the transition between two different dynamical states predicted for nonlinear systems.
Abstract: We performed a novel phase-sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and the nonlinear regime. When the junction was driven below the plasma frequency into the nonlinear regime, we observed for the first time the transition between two different dynamical states predicted for nonlinear systems. In our experiment, this transition appears as an abrupt change in the reflected signal phase at a critical excitation power. This controlled dynamical switching can form the basis of a sensitive amplifier, in particular, for the readout of superconducting qubits.
149 citations
TL;DR: In this article, an experimental observation of the backaction of a single-electron transistor (SET) measuring the Coulomb staircase of a box was presented. But the authors focused on the effects of quantum measurement on solid-state qubits.
Abstract: We report an experimental observation of the backaction of a single-electron transistor (SET) measuring the Coulomb staircase of a single-electron box. As current flows through the SET, the charge state of the SET island fluctuates. These fluctuations capacitively couple to the box and cause changes in the position, width, and asymmetry of the Coulomb staircase. A sequential tunneling model accurately recreates these effects, confirming this mechanism of the backaction of a SET. This is a first step toward understanding the effects of quantum measurement on solid-state qubits.
23 citations
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TL;DR: In this paper, an experimental observation of the backaction of a Single Electron Transistor (SET) measuring the Coulomb staircase of a single electron box was reported. But the experimental results were limited to a single box.
Abstract: We report an experimental observation of the backaction of a Single Electron Transistor (SET) measuring the Coulomb staircase of a single electron box. As current flows through the SET, the charge state of the SET island fluctuates. These fluctuations capacitively couple to the box and cause changes in the position, width, and asymmetry of the Coulomb staircase. A sequential tunnelling model accurately recreates these effects, confirming this mechanism of the backaction of an SET. This is a first step towards understanding the effects of quantum measurement on solid state qubits.
2 citations
TL;DR: In this article, the backaction of a superconducting single-electron transistor (SSET) continuously measuring a Cooper-pair box was investigated and a 2e periodic Coulomb staircase according to the two-level system Hamiltonian was observed.
Abstract: We investigate the backaction of superconducting single-electron transistor (SSET) continuously measuring a Cooper-pair box. Due to the minimized backaction of the SSET, we observe a 2e periodic Coulomb staircase according to the two-level system Hamiltonian of the Cooper-pair box. We demonstrate that we can control the quantum broadening of the ground state in-situ. We perform spectroscopy measurements and demonstrate that we have full control over the Cooper-pair box Hamiltonian. The ability to reduce the backaction is a necessary condition to use the SSET as a quantum state readout for the CPB as a qubit.
2 citations
TL;DR: In this article, a diffusion-engineered single-photon spectrometer was designed for the optical-UV range using a superconducting tunnel junction, where the optical photon is absorbed in a Ta film and creates excess quasiparticles.
Abstract: We have designed a diffusion-engineered, single-photon spectrometer in the optical-UV range using a superconducting tunnel junction. The optical photon is absorbed in a Ta film and creates excess quasiparticles. These trap into an Al tunnel junction. Internal charge multiplication is achieved with backtunneling, which occurs when the residence time of the quasiparticles near the junction is longer than the tunneling time. The collected charge is a multiple of the initially created charge. We implement backtunneling by geometrically constricting the outflow of quasiparticles, with a narrow lead. The outdiffusion time is set by the geometry of the narrow lead. Our geometry optimizes the energy resolution and count rate, while reducing the heating and noise seen with much longer confinement time. Long confinement times produce excess heating and noise, as we observed previously with quasiparticle confinement achieved via bandgap engineering.
1 citations
31 Aug 2005
TL;DR: Schuster et al. as mentioned in this paper developed a process for fabrication of Al/AlOx/Al tunnel qubits with integrated transmission line resonators, and used these devices for cavity-QED manipulations and readout of qubits.
Abstract: : This project supplies support for an additional graduate student, Mr. David Schuster, on experimental investigations on quantum coherence, entanglement, and quantum computation in solid-state, electronic realization of quantum bits based on superconducting single-electron devices, namely the single Cooper-pair box. Mr. Schuster has developed a process for fabrication of Al/AlOx/Al tunnel qubits with integrated transmission line resonators, and used these devices for cavity-QED manipulations and readout of qubits. This work has led to the first strong coupling of a solid-state qubit to a single photon, the first high-fidelity non-demolition readout of superconducting qubits, and the first high-visibility quantum control of superconducting qubits.