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Author |
Beck, M.; Klammer, M.; Rousseau, I.; Gol’tsman, G. N.; Diamant, I.; Dagan, Y.; Demsar, J. |
Title |
Probing superconducting gap dynamics with THz pulses |
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Conference Article |
Year |
2015 |
Publication |
CLEO |
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CLEO |
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SM3H.3 (1 to 2) |
Keywords |
superconducting gap; electric fields; femtosecond pulses; near infrared radiation; picosecond pulses; superconductors; thin films |
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We studied superconducting gap dynamics in a BCS superconductor NbN and electron doped cuprate superconductor PCCO following excitation with near-infrared (NIR) and narrow band THz pulses. Systematic studies on PCCO imply very selective electron-phonon coupling. |
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Optical Society of America |
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1345 |
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Takesue, Hiroki; Dyer, Shellee D.; Stevens, Martin J.; Verma, Varun; Mirin, Richard P.; Nam, Sae Woo |
Title |
Quantum teleportation over 100 km of fiber using highly efficient superconducting nanowire single-photon detectors |
Type |
Journal Article |
Year |
2015 |
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Optica |
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2 |
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Quantum teleportation is an essential quantum operation by which we can transfer an unknown quantum state to a remote location with the help of quantum entanglement and classical communication. Since the first experimental demonstrations using photonic qubits and continuous variables, the distance of photonic quantum teleportation over free-space channels has continued to increase and has reached >100 km. On the other hand, quantum teleportation over optical fiber has been challenging, mainly because the multifold photon detection that inevitably accompanies quantum teleportation experi- ments has been very inefficient due to the relatively low de- tection efficiencies of typical telecom-band single-photon detectors. Here, we report on quantum teleportation over optical fiber using four high-detection-efficiency supercon- ducting nanowire single-photon detectors (SNSPDs). These SNSPDs make it possible to perform highly efficient multi- fold photon measurements, allowing us to confirm that the quantum states of input photons were successfully tele- ported over 100 km of fiber with an average fidelity of 83.7 2.0%. |
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RPLAB @ alex_kazakov @ |
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1004 |
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Author |
Takemoto, K.; Nambu, Y.; Miyazawa, T.; Sakuma, Y.; Yamamoto, T.; Yorozu, S.; Arakawa, Y. |
Title |
Quantum key distribution over 120 km using ultrahigh purity single-photon source and superconducting single-photon detectors |
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Journal Article |
Year |
2015 |
Publication |
Sci. Rep. |
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5 |
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Pages |
14383 |
Keywords |
SSPD, SNSPD applications, quantum key distribution, QKD |
Abstract |
Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks. |
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Sidorova, Maria V.; Divochiy, Alexander; Vakhtomin, Yury B.; Smirnov, Konstantin V. |
Title |
Ultrafast superconducting single-photon detector with reduced-size active area coupled to a tapered lensed single-mode fiber |
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Conference Article |
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2015 |
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Proc. SPIE |
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9504 |
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950408 (1 to 9) |
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International Society for Optics and Photonics |
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RPLAB @ sasha @ sidorova2015ultrafast |
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1051 |
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Author |
Amundsen, Morten; Linder, Jacob |
Title |
General solution of 2D and 3D superconducting quasiclassical systems: coalescing vortices and nanodisk geometries |
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Journal Article |
Year |
2015 |
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arXiv:1512.00030 [cond-mat.supr-con] |
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quasiclassical Usadel equation, finite elements method |
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In quasiclassical Keldysh theory, the Green function matrix g<cb><2021> is used to compute a variety of physical quantities in mesoscopic systems. However, solving the set of non-linear differential equations that provide g<cb><2021> becomes a challenging task when going to higher spatial dimensions than one. Such an extension is crucial in order to describe physical phenomena like charge/spin Hall effects and topological excitations like vortices and skyrmions, none of which can be captured in one-dimensional models. We here present a numerical finite element method which solves the 2D and 3D quasiclassical Usadel equation, without any linearisation, relevant for the diffusive regime. We show the application of this on two model systems with non-trivial geometries: (i) a bottlenecked Josephson junction with external flux and (ii) a nanodisk ferromagnet deposited on top of a superconductor. We demonstrate that it is possible to control externally not only the geometrical array in which superconducting vortices arrange themselves, but also to cause coalescence and thus tune the number of vortices. The finite element method presented herein could pave the way for gaining insight in physical phenomena which so far have remained largely unexplored due to the complexity of solving the full quasiclassical equations in higher dimensions. |
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1066 |
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