Self-organized synthetic opals possessing a face centered cubic (fcc) lattice are promising for fabrication of a three-dimensional photonic crystal with a full photonic band gap in the visible. The fundamental limiting factor of this method is the large concentration of lattice defects and, especially, planar stacking faults, which are intrinsic to self-assembling growth of colloidal crystal. We have studied the influence of various types of defects on photonic band structure of synthetic opals by means of optical transmission, reflection and diffraction along different crystallographic directions. We found that in carefully chosen samples the stacking probability alpha can be as high as 0.8-0.9 revealing the strong preference of fcc packing sequence over the hexagonal close-packed (hcp). It is shown that scattering on plane stacking faults located perpendicular to the direction of growth results in a strong anisotropy of diffraction pattern as well as in appearance of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the direction of growth. This doublet is a direct manifestation of the coexistence of two crystallographic phases--pure fcc and strongly faulted. As a result the inhomogeneously broadened stop-bands overlap over a considerable amount of phase space. The latter, however, does not mean the depletion of the photonic density of states since large disordering results in filling of the partial gaps with both localized and extended states.

Optical spin-dynamic measurements in a high-mobility n-doped GaAs/AlGaAs quantum well show oscillatory evolution at 1.8 K consistent with a quasi-collision-free D'yakonov-Perel'-Kachorovskii regime. Above 5 K evolution becomes exponential as expected for collision-dominated spin dynamics. Momentum scattering times extracted from Hall mobility and Monte Carlo simulation of spin polarization agree at 1.8 K but diverge at higher temperatures, indicating the importance of electron-electron scattering and an intrinsic upper limit for the spin-relaxation rate.

Time-resolved optical measurements in (110)-oriented GaAs/AlGaAs quantum wells show a tenfold increase of the spin-relaxation rate as a function of applied electric field from 20 to 80 kV cm(-1) at 170 K and indicate a similar variation at 300 K, in agreement with calculations based on the Rashba effect. Spin relaxation is almost field independent below 20 kV cm(-1) reflecting quantum well interface asymmetry. The results indicate the achievability of a voltage-gateable spin-memory time longer than 3 ns simultaneously with a high electron mobility.

No abstract

We demonstrate an on-demand single-photon source that is compatible with standard telecom optical fiber. Through careful control of the critical strains of InAs∕GaAs self-assembled quantum dots, we produce a microcavity sample with a low density of large dots emitting into the fiber-optic transmission band at 1.3μm. The second-order correlation function of the source reveals a strong suppression in the rate of multiphoton pulses at both 5K and above 30K. The source may be useful for fiber-optic-based single-photon applications, such as quantum metrology, quantum communications, and distributed quantum computing.

We perform an all-optical spin-dynamic measurement of the Rashba spin-orbit interaction in ͑110͒-oriented GaAs/ AlGaAs quantum wells under applied electric field. This crystallographic orientation allows us to isolate the Rashba from other contributions, giving precise values of the Rashba coefficient. At low temperature, we find good agreement between our measurements and the k · p theory. Unexpectedly, we observe a temperature dependence of the Rashba coefficient that may signify the importance of higher-order terms of the Rashba coupling.

An electrically driven ∼1.3μm single-photon source is demonstrated. The source contains InAs quantum dots within a planar cavity light-emitting diode. Electroluminescence (EL) spectra show clear emission lines and from time resolved EL we estimate a primary decay time of ∼1ns. Time-varying Stark shifts are studied and proposed for truncating the emission in jitter-sensitive applications (optimization for 2ns detector gate width demonstrated) and for relaxing excitation pulse-length requirements. A correlation measurement demonstrates suppression of multiphoton emission to below 28% of the Poissonian level before correction for detector dark counts, suggesting g(2)(0)∼0.19 for the source itself.

We report the distribution of a cryptographic key, secure from photon number splitting attacks, over 35 km of optical fiber using single photons from an InAs quantum dot emitting ∼ 1.3 µm in a pillar microcavity. Using below GaAs-bandgap optical excitation, we demonstrate suppression of multiphoton emission to 10% of the Poissonian level without detector dark count subtraction. The source is incorporated into a phase encoded interferometric scheme implementing the BB84 protocol for key distribution over standard telecommunication optical fiber. We show a transmission distance advantage over that possible with (length-optimized) uniform intensity weak coherent pulses at 1310 nm in the same system. The majority of experimental realizations demonstrating quantum key distribution (QKD) have relied on encoding information onto weak coherent pulses (WCPs).1,2,3 Due to the Poissonian nature of laser light, there is a finite probability of generating two or more photons per pulse from such a source. This opens up a security threat where an eavesdropper, Eve, can take advantage of these extra photons by performing a photon number splitting (PNS) attack.4 To compensate for this security loophole, the transmitter, Alice, has to attenuate the signal by an amount that increases with distance, which reduces the transmission rate and ultimately limits the maximum secure transmission distance to the authorized recipient, Bob.5 Decoy-pulse techniques have been developed to help mitigate the risks associated with multiphoton pulse emission, 6,7 and PNS secure key distribution distances are now starting to exceed those achieved with uniform pulse intensities. 8A single quantum emitter will exhibit "anti-bunching" of the photon emission times, 9 such that a regulated stream of single photons with zero probability of emitting more than one photon in any given excitation pulse can be expected. Applying an efficient single quantum emitter in a cryptographic system would outperform all other methods developed to date. Several experiments using single photons with wavelengths compatible with silicon technology have already been used for QKD. These include using a stream of single-photon pulses generated by a single nitrogen-vacancy color center in a diamond 10 and emission from a quantum dot.11 Telecom wavelength QKD has been achieved by using pairs of photons produced via spontaneous parametric down conversion. 12,13In this letter we demonstrate QKD using an opticallyexcited, triggered single-photon source (SPS) emitting at a telecom wavelength. Our source, which shows a ten-fold reduction in multi-photon emission compared to a laser, has been used to distribute keys secure from the PNS attack over 35 km along standard optical fiber. By applying a security analysis for imperfect devices (GLLP), 14we demonstrate a transmission distance advantage compared to the same system configuration incorporating uniform intensity pulses from a laser source at the same wavelength.We have previously demonstrated that a low density of telecom waveleng...