78 research outputs found
Fabrication and characterization of superconducting circuit QED devices for quantum computation
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 10^4--10^6, 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 ebeam 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.Comment: 4 pages, 6 figures, Applied Superconductivity Conference 200
Hot Electron Bolometer Development for a Submillimeter Heterodyne Array Camera
We are developing Nb diffusion-cooled Hot Electron Bolometers (HEBs) for a
large-format array submillimeter camera. We have fabricated Nb HEBs using a new
angle deposition process. We have characterized these devices using heterodyne
mixing at 20 GHz. We also report on optimizations in the fabrication process
that improve device performance.Comment: 2005 International Symposium on Space Terahertz Technolog
Directional amplification with a Josephson circuit
Non-reciprocal devices, which have different transmission coefficients for
propagating waves in opposite directions, are crucial components in many low
noise quantum measurements. In most schemes, magneto-optical effects provide
the necessary non-reciprocity. In contrast, the proof-of-principle device
presented here, consists of two on-chip coupled Josephson parametric converters
(JPCs), which achieves directionality by exploiting the non-reciprocal phase
response of the JPC in the trans-gain mode. The non-reciprocity of the device
is controlled in-situ by varying the amplitude and phase difference of two
independent microwave pump tones feeding the system. At the desired working
point and for a signal frequency of 8.453 GHz, the device achieves a forward
power gain of 15 dB within a dynamical bandwidth of 9 MHz, a reverse gain of -6
dB and suppression of the reflected signal by 8 dB. We also find that the
amplifier adds a noise equivalent to less than one and a half photons at the
signal frequency (referred to the input). It can process up to 3 photons at the
signal frequency per inverse dynamical bandwidth. With a directional amplifier
operating along the principles of this device, qubit and readout preamplifier
could be integrated on the same chip.Comment: 7 pages, 5 figure
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