Security in quantum cryptography [1, 2] is continuously challenged by inventive attacks [3][4][5][6][7] targeting the real components of a cryptographic setup, and duly restored by new countermeasures [8][9][10] to foil them. Due to their high sensitivity and complex design, detectors are the most frequently attacked components. Recently it was shown that two-photon interference [11] from independent light sources can be exploited to avoid the use of detectors at the two ends of the communication channel [12,13]. This new form of detection-safe quantum cryptography, called Measurement-Device-Independent Quantum Key Distribution (MDI-QKD), has been experimentally demonstrated [13][14][15][16][17][18], but with modest delivered key rates.Here we introduce a novel pulsed laser seeding technique to obtain high-visibility interference from gain-switched lasers and thereby perform quantum cryptography without detector vulnerabilities with unprecedented bit rates, in excess of 1 Mb/s. This represents a 2 to 6 orders of magnitude improvement over existing implementations and for the first time promotes the new scheme as a practical resource for quantum secure communications. * marco.lucamarini@crl.toshiba.co.uk arXiv:1509.08137v2 [quant-ph] In Quantum Cryptography, a sender Alice transmits encoded quantum signals to a receiver Bob, who measures them and distils a secret string of bits with the sender via public discussion [1].Ideally, the use of quantum signals guarantees the information-theoretical security of the communication [2]. In practice, however, Quantum Cryptography is implemented with real components, which can deviate from the ideal description. This can be exploited to circumvent the quantum protection if the users are unaware of the problem [19].Usually the most complex components are also the most vulnerable. Therefore the vast majority of the attacks performed so far have targeted Bob's single photon detectors [3][4][5][6][7]. 13] is a recent form of Quantum Cryptography conceived to remove the problem of detector vulnerability. As depicted in Fig. 1(a), two light pulses are independently encoded and sent by Alice and Bob to a central node, Charlie. This is similar to a quantum access network configuration [20], but in MDI-QKD the central node does not need to be trusted and could even attempt to steal information from Alice and Bob. To follow the MDI-QKD protocol, Charlie must let the two light pulses interfere at the beam splitter inside his station and then measure them. The result can disclose the correlation between the bits encoded by the users, but not their actual values, which therefore remain secret. If Charlie violates the protocol and measures the pulses separately, he can learn the absolute values of the bits, but not their correlation. Therefore he cannot announce the correct correlation to the users, who will then unveil his attempt through public discussion.Irrespective of Charlie's choice, the users' apparatuses no longer need a detector and the detection vulnerability of Quantum Cryp...

The reaction of laser-ablated Al atoms and normal-H(2) during co-deposition at 3.5 K produces AlH, AlH(2), and AlH(3) based on infrared spectra and the results of isotopic substitution (D(2), H(2) + D(2) mixtures, HD). Four new bands are assigned to Al(2)H(4) from annealing, photochemistry, and agreement with frequencies calculated using density functional theory. Ultraviolet photolysis markedly increases the yield of AlH(3) and seven new absorptions for Al(2)H(6) in the infrared spectrum of the solid hydrogen sample. These frequencies include terminal Al-H(2) and bridge Al-H-Al stretching and AlH(2) bending modes, which are accurately predicted by quantum chemical calculations for dibridged Al(2)H(6), a molecule isostructural with diborane. Annealing these samples to remove the H(2) matrix decreases the sharp AlH(3) and Al(2)H(6) absorptions and forms broad 1720 +/- 20 and 720 +/- 20 cm(-1) bands, which are due to solid (AlH(3))(n). Complementary experiments with thermal Al atoms and para-H(2) at 2.4 K give similar spectra and most product frequencies within 2 cm(-1). Although many volatile binary boron hydride compounds are known, binary aluminum hydride chemistry is limited to the polymeric (AlH(3))( solid. Our experimental characterization of the dibridged Al(2)H(6) molecule provides an important link between the chemistries of boron and aluminum.

We describe the construction and operation of a catalyst-bed type device for precooling and equilibrating the ortho/para composition of a hydrogen gas flow. We use this device to vapor deposit millimeters thick cryogenic parahydrogen (pH2) solids which are remarkably transparent [M. E. Fajardo and S. Tam, J. Chem. Phys. 108, 4237 (1998)]. Infrared absorption spectra of solids deposited at pH2 flow rates up to 290 mmol/h (solid thickness growth rates up to 75 μm/min indicate a residual orthohydrogen (oH2) content of less than 0.01%. Gas phase thermal conductivity measurements indicate a residual oH2 content of 0(−0+5)% for flow rates up to 1.9 mol/h. These pH2 solids can be doped readily by simple codeposition of various impurities produced by any of the numerous dopant sources developed in previous matrix isolation spectroscopy (MIS) studies. The long achievable path lengths, and the desirable properties of pH2 as a matrix host, will enable significant new fundamental and practical applications for MIS.

Structural and optical properties of sol-gel derived nanocrystalline Fe-doped ZnOSimple ortho-para hydrogen and para-ortho deuterium converter for matrix isolation spectroscopy Rev. Sci. Instrum. 75, 3039 (2004); 10.1063/1.1786332 Low temperature deposition of nanocrystalline silicon carbide films by plasma enhanced chemical vapor deposition and their structural and optical characterization J. Appl. Phys. 94, 5252 (2003); 10.1063/1.1609631Ortho/para hydrogen converter for rapid deposition matrix isolation spectroscopy Rev.We report the rapid vapor deposition of millimeters thick parahydrogen (pH 2 ) solids of remarkable optical clarity. Characterization of pure pH 2 samples by IR and Raman spectra show a very low orthohydrogen and vacancy content, and a mixed hexagonal-closed-packed/face-centered-cubic ͑hcp/fcc͒ polycrystalline structure for as-deposited samples, which converts to hcp upon annealing. Efficient isolation of atomic and molecular dopants is achieved by conventional matrix isolation spectroscopy ͑MIS͒ techniques. The increased optical path lengths offer significant improvements in spectroscopic data quality, and reveal novel dopant-induced IR absorptions of the pH 2 matrix host itself. Thus, while traditional MIS studies in rare gas hosts can only probe the influence of the matrix environment on the spectrum of the dopant ''solute,'' in pH 2 the response of the host ''solvent'' is directly observable as well. This complementary information may prove to be the key to identifying conclusively the microscopic structures of dopant trapping sites.

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