- Circuit quantum electrodynamics
We have built an integrated circuit in which a superconducting qubit,
or artificial atom, is coupled to a single microwave photon trapped in a
superconducting transmission line cavity. It has direct analogies with
the field of cavity quantum electrodynamics (cavity QED) in quantum
- cQED publications
- Investigators: Andrei Petrenko, Matthew Reagor, Eric Holland, Brian Vlastakis, Adam Sears, Matthew Reed, Nissim Ofek, Gerhard Kirchmair, Luyan Sun, Luigi Frunzio, Rob Schoelkopf
- Cold Molecules and Quantum Computation
Isolated molecular systems are unique for their exceptional coherence
properties, making them excellent candidates for quantum information
applications. We would like to implement a coupled molecule-superconducting
on-chip cavity system at microwave frequencies. Polar molecules like CaF,
CaBr possess rotational energy levels in the microwave frequencies regime,
which make them suitable for strong coupling to a superconducting stripline
Through the Stark interaction of the molecular dipoles with applied static
electric fields, polar molecules of certain rotational states can be trapped
in localized field minima produced by electrostatic electrodes in planar
geometries. Molecules trapped in proximity to the surface of a
superconducting stripline resonator can be strongly coupled and residual
motional energy of the molecules can be removed through dissipation into the
cavity (sideband cooling). A microwave dispersive measurement similar to
that done in our qubit-resonator systems can then be performed on the
molecule rotational state.
- Investigators: Andreas Fragner, Rob Schoelkopf
- Shot Noise Thermometry
We are developing a primary thermometer based on the thermal and shot noise of current flowing through a Josephson junction which can be fabricated by electron beam or optical lithography. Measurements of shot noise at high current are used to calibrate the measurement of the thermal noise. This calibrated measurement can then be used to determine the temperature based only fundamental physical laws and constants. In addition the temperature can be determined accurately over a wide dynamic range from mK to room temperature. This technique could potentially obtain metrological precision and be used by itself or to calibrate other conventional secondary thermometers.
- See out list of shot noise thermometer publications
- Single-photon counters for submillimeter astronomy
We are developing superconducting direct detectors (the Single Quasiparticle Photon Counter, or SQPC) for submillimeter astronomy that can in principle detect individual photons. The SQPC uses a small (~100 micron) antenna to couple the energy of submillimeter photons into a small superconducting Aluminum absorber, where it breaks Cooper pairs. These excitations then tunnel through a superconducting tunnel junction and are read-out as a photocurrent. Furthermore, if coupled to a Radio-Frequency Single Electron Transistor (RF-SET), one might have not only the sensitivity, but also the bandwidth to resolve individual photons. We are currently collaborating with NASA Goddard to make and test these detectors.
- Radio Frequency Single Electron Transistor (RF-SET)
A Single Electron Transistor (SET) is a mesoscopic device consisting of two tunnel junctions in series. They utilize the Coulomb Blockade effect to act as an exquisitely sensitive electrometer. The conductivity of the SET can be modulated by effective charges that are a small fraction of the electron charge. In conventional SET's this change in conductivity is determined by measuring the current through the device at constant voltage. Because the SET is high-impedance and the readout has high capacitance conventional SET's have very poor time resolution (bandwidth ~1kHz). The RF-SET is a modification of the SET design which determines the conductivity by shining microwave radiation on the device and measuring the reflected power. This can be done very quickly (bandwidth ~50-100 MHz) which allows us to study the dynamics of single electron process which were previously inaccessible.