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Two protocols of quantum direct communication with authentication [Phys. Rev. A 73 (2006) 042305] were recently indicated to be insecure against the authenticator Trent attacks [Phys. Rev. A 75 (2007) 026301]. We present two efficient protocols by using four Pauli operations, which are secure against inner Trent attacks as well as outer Eve attacks. Finally we generalize them to multiparty quantum direction communication. [ABSTRACT FROM AUTHOR]

A class of unlockable bound entangled states and their applications are presented. They can be considered as quasi generalized Smolin states [Phys. Rev. A 63 (2001) 032306], which are the states of N + N qubits. No pure entanglement can be distilled from this class of states by local quantum operations and classical communications. However, if certain parties group together, they become distillable. Although they are bound entangled states, they could be used to achieve some non-trivial tasks, such as quantum secret sharing shown in the study. [ABSTRACT FROM AUTHOR]

A 32 Gb/s monolithically integrated electroabsorption modulated laser is fabricated by selective area growth technology. The threshold current of the device is below 13 mA. The output power exceeds 10 mW at 0 V bias when the injection current of the distributed feedback laser is 100 mA at 25°C. The side mode suppression ratio is over 50 dB. A 32Gb/s eye diagram is measured with a 3.5Vpp nonreturn-to-zero pseudorandom modulation signal at −2.3 V bias. A clearly opening eyediagram with a dynamic extinction ratio of 8.01 dB is obtained. [ABSTRACT FROM AUTHOR]

We report on the acousto-optic Q-switched operation of a Ho:YAP laser double-passed pumped by an all-fiber Tm-doped fiber laser. The output characteristics of the Ho:YAP laser are studied at pulse repetition frequencies of 1, 2, 5 and 10 kHz. The shortest pulse width, the maximum pulse energy and the highest peak power are measured to be 17 ns, 1.71 mJ and 71.25 kW, respectively. The output wavelength is centered at 2115.96 nm with a bandwidth of about 1.5 nm. The beam quality factor M2 = 2.41 +- 0.03 at the output power of 3.54 W was measured by using the traveling knife-edge method. [ABSTRACT FROM AUTHOR]

We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors of 2 and 3, respectively. For N([?]3)-period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum-memory-based long-distance fiber communication systems. [ABSTRACT FROM AUTHOR]

We present a wavelength-tunable narrow-band fiber-coupled source to generate correlated photon pairs at 539nm and 1550nm. Using a 10-mm PPLN crystal, we obtain more than 50mm tunable range near 1550nm. This source, given its spectral property and tunable property, is well suited for tasks in fiber-optic quantum communication and cryptography networks. [ABSTRACT FROM AUTHOR]

A novel integratable and high speed InGaAsP multi-quantum well (MQW) complex-coupled distributed feedback (DFB) laser is successfully fabricated on a semi-insulating substrate. The fabricated ridge DFB laser exhibits a threshold current of 26 mA, a slope efficiency of 0.14 W.A[?]1 and a side mode suppression ratio of 40 dB together with a 3 dB bandwidth of more than 8 GHz. The device is suitable for 10 Gbit/s optical fiber communication. [ABSTRACT FROM AUTHOR]