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Bialczak, R. C.; Ansmann, M.; Hofheinz, M.; Lucero, E.; Neeley, M.; O'Connell, A. D.; Sank, D.; Wang, H.; Wenner, J.; Steffen, M.; Cleland, A. N.; Martinis, J. M. |
| Title |
Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits |
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Journal Article |
| Year |
2010 |
Publication |
Nature Physics |
Abbreviated Journal |
Nat. Phys. |
| Volume |
6 |
Issue |
6 |
Pages  |
409-413 |
| Keywords |
fromIPMRAS |
| Abstract |
Quantum gates must perform reliably when operating on standard input basis states and on complex superpositions thereof. Experiments using superconducting qubits have validated truth tables for particular implementations of, for example, the controlled-NOT gate, but have not fully characterized gate operation for arbitrary superpositions of input states. Here we demonstrate the use of quantum process tomography (QPT) to fully characterize the performance of a universal entangling gate between two superconducting qubits. Process tomography permits complete gate analysis, but requires precise preparation of arbitrary input states, control over the subsequent qubit interaction and ideally simultaneous single-shot measurement of output states. In recent work, it has been proposed to use QPT to probe noise properties and time dynamics of qubit systems and to apply techniques from control theory to create scalable qubit benchmarking protocols. We use QPT to measure the fidelity and noise properties of an entangling gate. In addition to demonstrating a promising fidelity, our entangling gate has an on-to-off ratio of 300, a level of adjustable coupling that will become a requirement for future high-fidelity devices. This is the first solid-state demonstration of QPT in a two-qubit system, as QPT has previously been demonstrated only with single solid-state qubits. |
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Konstantatos, Gerasimos; Sargent, Edward H. |
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Nanostructured materials for photon detection |
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Journal Article |
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2010 |
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Nature Nanotechnology |
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Nat. Nanotech. |
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5 |
Issue |
6 |
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391–400 |
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The detection of photons underpins imaging, spectroscopy, fibre-optic communications and time-gated distance measurements. Nanostructured materials are attractive for detection applications because they can be integrated with conventional silicon electronics and flexible, large-area substrates, and can be processed from the solution phase using established techniques such as spin casting, spray coating and layer-by-layer deposition. In addition, their performance has improved rapidly in recent years. Here we review progress in light sensing using nanostructured materials, focusing on solution-processed materials such as colloidal quantum dots and metal nanoparticles. These devices exhibit phenomena such as absorption of ultraviolet light, plasmonic enhancement of absorption, size-based spectral tuning, multiexciton generation, and charge carrier storage in surface and interface traps. |
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Tikhonov, V. V.; Boyarskii, D. A.; Polyakova, O. N.; Dzardanov, A. L.; Goltsman, G. N. |
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Radiophysical and dielectric properties of ore minerals in 12--145 GHz frequency range |
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Journal Article |
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2010 |
Publication |
PIER B |
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PIER B |
| Volume |
25 |
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349-367 |
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complex permittivity, ore minerals |
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The paper discusses a retrieval technique of complex permittivity of ore minerals in frequency ranges of 12--38 GHz and 77--145 GHz. The method is based on measuring frequency dependencies of transmissivity and reflectivity of plate-parallel mineral samples. In the 12--38 GHz range, the measurements were conducted using a panoramic standing wave ratio and attenuation meter. In the 77--145 GHz range, frequency dependencies of transmissivity and reflectivity were obtained using millimeter-band spectrometer with backward-wave oscillators. The real and imaginary parts of complex permittivity of a mineral were determined solving an equation system for frequency dependencies of transmissivity and reflectivity of an absorbing layer located between two dielectric media. In the course of the work, minerals that are primary ores in iron, zinc, copper and titanium mining were investigated: magnetite, hematite, sphalerite, chalcopyrite, pyrite, and ilmenite. |
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639 |
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Churikov, Victor M.; Kopp, Victor I.; Genack, Azriel Z. |
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Chiral diffraction gratings in twisted microstructured fibers |
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Journal Article |
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2010 |
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Optics Letters |
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Opt. Lett. |
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35 |
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3 |
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342-344 |
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chiral diffracion gratings, optical fiber gratings, from chiralphotonics |
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We observed dips in transmission spectra of uniformly twisted pure-silica microstructured fibers. The spectral positions of the dips and their insensitivity to the surrounding medium are consistent with Bragg diffraction from the helical structure. The reproducibility of the variation of the dip wavelength with temperature up to 1000°C makes the chiral diffraction grating suitable for high-temperature sensing. |
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853 |
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Yamashita, Taro; Miki, Shigehito; Qiu, Wei; Fujiwara, Mikio; Sasaki, Masahide; Wang, Zhen |
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Temperature dependent performances of superconducting nanowire single-photon detectors in an ultralow-temperature region |
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Journal Article |
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2010 |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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336 - 339 |
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SNSPD |
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We report on the performance of a fiber-coupled superconducting nanowire single-photon detector (SNSPD) from 4 K down to the ultralow temperature of 16 mK for a 1550 nm wave length. The system detection efficiency (DE) increased with de creasing the temperature and reached the considerably high value of 15% with a dark count rate less than 100 cps below 1.5 K, even without an optical cavity structure. We also observed saturation of the system DE in its bias current dependency at 16 mK, which indicates that the device DE of our SNSPD nearly reached intrinsic DE despite the device having a large active area of 20 μm × 20 μm. The dark count was finite even at 16 mK and the black body radiation becomes its dominant origin in the low temperatures for fiber-coupled devices. |
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