Quantum computing and condensed matter physics with microwave photons

Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy

H. Malissa, D. I. Schuster, A. M. Tyryshkin, A. A. Houck, S. A. Lyon

We discuss the design and implementation of thin film superconducting coplanar waveguide micro- resonators for pulsed ESR experiments. The performance of the resonators with P doped Si epilayer samples is compared to waveguide resonators under equivalent conditions. The high achievable filling factor even for small sized samples and the relatively high Q-factor result in a sensitivity that is superior to that of conventional waveguide resonators, in particular to spins close to the sample surface.

Coherent control of a superconducting qubit with dynamically tunable qubit-cavity coupling

A. J. Hoffman, S. J. Srinivasan, J. M. Gambetta, and A. A. Houck

We demonstrate coherent control and measurement of a superconducting qubit coupled to a superconducting coplanar waveguide resonator with a dynamically tunable qubit-cavity coupling strength. Rabi oscillations are measured for several coupling strengths showing that the qubit transition can be turned off by a factor of more than 1500. We show how the qubit can still be accessed in the off state via fast flux pulses.

Dispersive Photon Blockade in a Superconducting Circuit

A. J. Hoffman, S. J. Srinivasan, S. Schmidt, L. Spietz, J. Aumentado, H. E. Türeci, and A. A. Houck

Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots.

Tunable Coupling in Circuit Quantum Electrodynamics Using a Superconducting Charge Qubit with a V-Shaped Energy Level Diagram

S. J. Srinivasan, A. J. Hoffman, J. M. Gambetta, and A. A. Houck

We introduce a new type of superconducting charge qubit that has aV-shaped energy spectrum and uses quantum interference to provide independently tunable qubit energy and coherent coupling to a superconducting cavity. Dynamic access to the strong coupling regime is demonstrated by tuning the coupling strength from less than 200 kHz to greater than 40 MHz. This tunable coupling can be used to protect the qubit from cavity-induced relaxation and avoid unwanted qubit-qubit interactions in a multiqubit system.

Superconducting Qubit with Purcell Protection and Tunable Coupling

J. M. Gambetta, A. A. Houck, and Alexandre Blais

We present a superconducting qubit for the circuit quantum electrodynamics architecture that has a tunable qubit-resonator coupling strengthg. This coupling can be tuned from zero to values that are comparable with other superconducting qubits. At g=0, the qubit is in a decoherence-free subspace with respect to spontaneous emission induced by the Purcell effect. Furthermore, we show that in this decoherence-free subspace, the state of the qubit can still be measured by either a dispersive shift on the resonance frequency of the resonator or by a cycling-type measurement.

Quantum Non-demolition Detection of Single Microwave Photons in a Circuit

B. R. Johnson, M. D. Reed, A. A. Houck, D. I. Schuster, Lev S. Bishop, E. Ginossar, J. M. Gambetta, L. DiCarlo, L. Frunzio, S. M. Girvin, R. J. Schoelkopf

Thorough control of quantum measurement is key to the development of quantum information technologies. Many measurements are destructive, removing more information from the system than they obtain. Quantum non-demolition (QND) measurements allow repeated measurements that give the same eigenvalue. They could be used for several quantum information processing tasks such as error correction, preparation by measurement, and one-way quantum computing.