Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N1: Superconducting Qubits |
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Sponsoring Units: DCMP Chair: John Martinis, UCSB Room: LACC 152 |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N1.00001: Coherent Dynamics of a flux-qubit coupled to a harmonic oscillator Invited Speaker: Superconducting circuits containing Josephson junctions are promising candidates for the implementation of solid-state quantum bits or qubits. Complex single-qubit operations have already been reported, as well as the realization of a two-qubit gate. Coupling a qubit to a harmonic oscillator is interesting from a fundamental point of view to generate and study non-classical states of the oscillator, and is relevant in quantum information as well, since coupling many qubits via a harmonic oscillator has been proposed. The strong coupling between a charge qubit and a superconducting coplanar waveguide resonator has recently been observed [1]. Here we present measurements demonstrating the coupling of a flux-qubit to the plasma mode of the DC Squid which at the same time is used to measure the qubit state [2]. This coupling is manifested by the appearance of two side-band resonances around the bare qubit peak. By performing two-pulse experiments, we show that these additional resonances are indeed excitations of the coupled system. We also observe Rabi oscillations between the coupled $\vert $qubit,Squid$>$ states, thus demonstrating entanglement between the states of two superconducting circuits. We use the qubit to measure intrinsic properties of the plasma mode : temperature, relaxation time. Conversely, we also measure the qubit state via the plasma mode. We finally investigate the influence of the qubit-plasma mode coupling on the qubit quantum coherence. These results indicate that complex manipulation of entangled states similar to cavity quantum electrodynamics or trapped-ions experiments is within reach with superconducting circuits. [1] A. Wallraff et al., Nature \textbf{431}, 162 (2004) [2] I. Chiorescu et al., Nature \textbf{431}, 159 (2004) . [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N1.00002: Continuous Impedance measurement of a Superconducting Flux Qubit Invited Speaker: We implement the radio-frequency technique for characterization of superconducting qubits and for measuring their states. In the framework of this method, the qubit is inductively coupled to a high-quality tank circuit. We show that this technique is a powerful tool to study a response of externally controlled superconducting qubit to different types of excitations. Conclusive information about qubits is obtained from the read out of the tank properties. We also show that the tank circuit can be effectively used to monitor an adiabatic evolution of the superconducting flux qubits. By making use the radio- frequency technique the qubit's state can be determined, moreover such kind of measurements belong to the class of quantum nondemolition measurement. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:48AM |
N1.00003: Circuit Quantum Electrodynamics: A New Architecture for Superconducting Quantum Computation Invited Speaker: I will describe recent experiments in which the strong coupling limit of cavity quantum electrodynamics has been realized for the first time using superconducting circuits [1]. In our approach, we use a Cooper-pair box as an artificial atom, which is coupled to a one-dimensional cavity formed by a transmission line resonator. In the case when the Cooper-pair box qubit is tuned into resonance with the cavity, we observe the vacuum Rabi splitting of the cavity mode, indicating that the strong coupling regime is attained, and coherent superpositions between the qubit and a single photon are generated. When the qubit is detuned from the cavity resonance frequency, we perform high-fidelity dispersive quantum non-demolition readout of the qubit state. Using this readout technique, we have characterized the qubit properties spectroscopically, performed Rabi oscillations of the qubit, and attained coherence times greater than 500 ns, indicating that this architecture is extremely attractive for quantum computing and control [2].\par [1] A. Wallraff, D. I. Schuster, A. Blais, L. Frunzio, R.-S. Huang, J. Majer, S. Kumar, S. M. Girvin and R. J. Schoelkopf Nature (London) \textbf{431}, 162 (2004)\par [2] A. Blais, R.-S. Huang, A. Wallraff, S. M. Girvin and R. J. Schoelkopf Phys. Rev. A \textbf{69}, 062320 (2004)\par [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:24AM |
N1.00004: Single-Shot State Measurement of Coupled Phase Qubits Invited Speaker: A major reason that superconducting Josephson tunnel junctions are promising quantum bit (qubit) candidates for a quantum computer is their potential for scalability using conventional integrated-circuit technology. We have taken a first step toward implementing multi-qubit systems by fabricating pairs of capacitively coupled Josephson phase qubits with individual control and measurement circuitry. Spectroscopic measurements verify that the two qubits become coupled when they are tuned into resonance with each other. Furthermore, with the benefit of a fast state measurement technique, we are able to perform simultaneous single-shot measurements of the two qubits individually. The success of these experiments relies on an understanding of classical measurement crosstalk, where the readout of one qubit may cause unwanted transitions in the second qubit. Because the crosstalk does not occur instantaneously, it can be largely avoided by timing the separate qubit measurements to be coincident. Time-domain experiments reveal antiphase oscillations between the two-qubit basis states $|01\rangle$ and $|10\rangle$, with the frequency of oscillation determined by the engineered capacitive coupling strength between the two qubits. These results are consistent with quantum mechanical entanglement of the two qubits, and they open the possibility for the characterization of multi-qubit gates and elementary quantum algorithms. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 11:00AM |
N1.00005: Superconducting Flux Qubits Invited Speaker: This abstract was not received electronically. [Preview Abstract] |
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