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| Author |
Ghali, Mohsen; Ohtani1, Keita; Ohno, Yuzo; Ohno, Hideo |
| Title |
Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field |
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Journal Article |
| Year |
2012 |
Publication |
Nature Communications |
Abbreviated Journal  |
Nat. Comm. |
| Volume |
3 |
Issue |
661 |
Pages |
6 |
| Keywords |
fromIPMRAS |
| Abstract |
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05. |
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RPLAB @ gujma @ |
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769 |
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Grotz, Bernhard; Hauf, Moritz V.; Dankerl, Markus; Naydenov, Boris; Pezzagna, Sébastien; Meijer, Jan; Jelezko, Fedor; Wrachtrup, Jörg; Stutzmann, Martin; Reinhard, Friedemann; Garrido, Jose A. |
| Title |
Charge state manipulation of qubits in diamond |
Type |
Journal Article |
| Year |
2012 |
Publication |
Nature Communications |
Abbreviated Journal |
Nat. Comm. |
| Volume |
3 |
Issue |
729 |
Pages |
6 |
| Keywords |
fromIPMRAS |
| Abstract |
The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV- into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV0, and the population of an ensemble of centres can be shifted from NV0 to NV-. Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV+. |
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RPLAB @ gujma @ |
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770 |
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Kumar, Sushil; Chan, Chun Wang I.; Hu, Qing; Reno, John L. |
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A 1.8-THz quantum cascade laser operating significantly above the temperature of hw/k |
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Journal Article |
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2011 |
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Nature Physics |
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7 |
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166-171 |
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QCL, 2 mW at 155 K and 1.8 THz |
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Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~planckω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9planckω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser. |
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631 |
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Williams, Benjamin S. |
| Title |
Terahertz quantum-cascade lasers |
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Journal Article |
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2007 |
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Nature Photonics |
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1 |
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517-525 |
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QCL review |
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Six years after their birth, terahertz quantum-cascade lasers can now deliver milliwatts or more of continuous-wave coherent radiation throughout the terahertz range — the spectral regime between millimetre and infrared wavelengths, which has long resisted development. This paper reviews the state-of-the-art and future prospects for these lasers, including efforts to increase their operating temperatures, deliver higher output powers and emit longer wavelengths. |
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632 |
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Tang, Liang; Kocabas, Sukru Ekin; Latif, Salman; Okyay, Ali K.; Ly-Gagnon, Dany-Sebastien; Saraswat, Krishna C.; Miller, David A. B. |
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Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna |
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2008 |
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Nature Photonics |
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2 |
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226-229 |
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optical antennas |
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A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise. A photodetector can be made smaller by using a subwavelength active region; however, this can result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a half-wave Hertz dipole antenna (length approx 380 nm) from radio waves, but at near-infrared wavelengths (length approx 1.3 microm), to concentrate radiation into a nanometre-scale germanium photodetector. This gives a polarization contrast of a factor of 20 in the resulting photocurrent in the subwavelength germanium element, which has an active volume of 0.00072 microm3, a size that is two orders of magnitude smaller than previously demonstrated detectors at such wavelengths. |
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858 |
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Collins, M. J.; Xiong, C.; Rey, I. H.; Vo, T. D.; He, J.; Shahnia, S.; Reardon, C.; Krauss, T. F.; Steel, M. J.; Clark, M.J.; & Eggleton, B.J. |
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Integrated spatial multiplexing of heralded single-photon sources |
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Journal Article |
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2013 |
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Nature Communications |
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The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the her- alded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon inter- ference, required at the core of optical quantum computing and quantum communication protocols. |
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English |
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RPLAB @ alex_kazakov @ |
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1001 |
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