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Bylander, Jonas; Gustavsson, Simon; Yan, Fei; Yoshihara, Fumiki; Harrabi, Khalil; Fitch, George; Cory, David G.; Nakamura, Yasunobu; Tsai, Jaw-Shen; Oliver, William D. |
| Title |
Noise spectroscopy through dynamical decoupling with a superconducting flux qubit |
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Journal Article |
| Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
| Volume |
7 |
Issue |
7 |
Pages |
565-570 |
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fromIPMRAS |
Abstract  |
Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1=12μs. We first demonstrate that dynamical decoupling improves the coherence time T2 in this system up to the T2=2T1 limit (pure dephasing times exceeding 100μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20MHz, observing a 1/fα distribution with α<1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence. |
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829 |
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Mitin, Vladimir; Antipov, Andrei; Sergeev, Andrei; Vagidov, Nizami; Eason, David; Strasser, Gottfried |
| Title |
Quantum Dot Infrared Photodetectors: Photoresponse Enhancement Due to Potential Barriers |
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Journal Article |
| Year |
2011 |
Publication |
Nanoscale Research Letters |
Abbreviated Journal |
Nanoscale res lett |
| Volume |
6 |
Issue |
1 |
Pages |
6 |
| Keywords |
Quantum dots; Infrared detectors; Photoresponse; Doping; Potential barriers; Capture processes |
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Potential barriers around quantum dots (QDs) play a key role in kinetics of photoelectrons. These barriers are always created, when electrons from dopants outside QDs fill the dots. Potential barriers suppress the capture processes of photoelectrons and increase the photoresponse. To directly investigate the effect of potential barriers on photoelectron kinetics, we fabricated several QD structures with different positions of dopants and various levels of doping. The potential barriers as a function of doping and dopant positions have been determined using nextnano3 software. We experimentally investigated the photoresponse to IR radiation as a function of the radiation frequency and voltage bias. We also measured the dark current in these QD structures. Our investigations show that the photoresponse increases ~30 times as the height of potential barriers changes from 30 to 130 meV. |
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712 |
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Peruzzo, Alberto; Laing, Anthony; Politi, Alberto; Rudolph, Terry; O'Brien, Jeremy L. |
| Title |
Multimode quantum interference of photons in multiport integrated devices |
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Journal Article |
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2011 |
Publication |
Nature Communications |
Abbreviated Journal |
Nat. Comm. |
| Volume |
2 |
Issue |
224 |
Pages |
6 |
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fromIPMRAS |
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Photonics is a leading approach in realizing future quantum technologies and recently, optical waveguide circuits on silicon chips have demonstrated high levels of miniaturization and performance. Multimode interference (MMI) devices promise a straightforward implementation of compact and robust multiport circuits. Here, we show quantum interference in a 2×2 MMI coupler with visibility of V=95.6+/-0.9%. We further demonstrate the operation of a 4×4 port MMI device with photon pairs, which exhibits complex quantum interference behaviour. We have developed a new technique to fully characterize such multiport devices, which removes the need for phase-sensitive measurements and may find applications for a wide range of photonic devices. Our results show that MMI devices can operate in the quantum regime with high fidelity and promise substantial simplification and concatenation of photonic quantum circuits. |
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763 |
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Fazal, Furqan M.; Block, Steven M. |
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Optical tweezers study life under tension |
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Journal Article |
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2011 |
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Nature Photonics |
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Nat. Photon. |
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5 |
Issue |
6 |
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318-321 |
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Optical tweezers have become one of the primary weapons in the arsenal of biophysicists, and have revolutionized the new field of single-molecule biophysics. Today's techniques allow high-resolution experiments on biological macromolecules that were mere pipe dreams only a decade ago. |
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RPLAB @ gujma @ |
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776 |
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Hu, Xiaolong; Dauler, Eric A.; Molnar, Richard J.; Berggren, Karl K. |
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Superconducting nanowire single-photon detectors integrated with optical nano-antennae |
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Journal Article |
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2011 |
Publication |
Optics Express |
Abbreviated Journal |
Opt. Express |
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19 |
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1 |
Pages |
17-31 |
| Keywords |
optical antennas |
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Optical nano-antennae have been integrated with semiconductor lasers to intensify light at the nanoscale and photodiodes to enhance photocurrent. In quantum optics, plasmonic metal structures have been used to enhance nonclassical light emission from single quantum dots. Absorption and detection of single photons from free space could also be enhanced by nanometallic antennae, but this has not previously been demonstrated. Here, we use nano-optical transmission effects in a one-dimensional gold structure, combined with optical cavity resonance, to form optical nano-antennae, which are further used to couple single photons from free space into a 80-nm-wide superconducting nanowire. This antenna-assisted coupling enables a superconducting nanowire single-photon detector with 47% device efficiency at the wavelength of 1550 nm and 9-μm-by-9-μm active area while maintaining a reset time of only 5 ns. We demonstrate nanoscale antenna-like structures to achieve exceptional efficiency and speed in single-photon detection. |
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RPLAB @ gujma @ |
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745 |
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