6 research outputs found
Self-referenced continuous-variable quantum key distribution protocol
We introduce a new continuous-variable quantum key distribution (CV-QKD)
protocol, self-referenced CV-QKD, that eliminates the need for transmission of
a high-power local oscillator between the communicating parties. In this
protocol, each signal pulse is accompanied by a reference pulse (or a pair of
twin reference pulses), used to align Alice's and Bob's measurement bases. The
method of phase estimation and compensation based on the reference pulse
measurement can be viewed as a quantum analog of intradyne detection used in
classical coherent communication, which extracts the phase information from the
modulated signal. We present a proof-of-principle, fiber-based experimental
demonstration of the protocol and quantify the expected secret key rates by
expressing them in terms of experimental parameters. Our analysis of the secret
key rate fully takes into account the inherent uncertainty associated with the
quantum nature of the reference pulse(s) and quantifies the limit at which the
theoretical key rate approaches that of the respective conventional protocol
that requires local oscillator transmission. The self-referenced protocol
greatly simplifies the hardware required for CV-QKD, especially for potential
integrated photonics implementations of transmitters and receivers, with
minimum sacrifice of performance. As such, it provides a pathway towards
scalable integrated CV-QKD transceivers, a vital step towards large-scale QKD
networks.Comment: 14 pages, 10 figures. Published versio
Metropolitan quantum key distribution with silicon photonics
Photonic integrated circuits (PICs) provide a compact and stable platform for
quantum photonics. Here we demonstrate a silicon photonics quantum key
distribution (QKD) transmitter in the first high-speed polarization-based QKD
field tests. The systems reach composable secret key rates of 950 kbps in a
local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 106
kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss).
Our results represent the highest secret key generation rate for
polarization-based QKD experiments at a standard telecom wavelength and
demonstrate PICs as a promising, scalable resource for future formation of
metropolitan quantum-secure communications networks
Ultrafast carrier dynamics in semiconductor self-assembled quantum dots in the low carrier density regime.
Self-assembled quantum dots are nanoscopic clusters of semiconductor atoms that exhibit atom-like properties because of their three dimensional quantum confining potentials. The quantum confinement offered by quantum dots is expected to reap benefits for many optoelectronic applications. In fact, high performance lasers and detectors based on quantum dots are already being developed. For these applications as well as for those with new functionalities, one of the most critical factors affecting performance will be relaxation processes of the carriers. Thus in order to fully exploit the benefits of self-assembled quantum dots, one must have a clear understanding of the physical mechanisms that govern carrier dynamics. Ultrafast carrier dynamics which occur on the time scales of femtoseconds and picoseconds among the quantum dots at low densities are the topics of this thesis. A femtosecond differential transmission pump-probe technique is employed to time-resolve directly the carrier distribution among an ensemble of multilayer self-assembled quantum dots. Measurements show that in multilayer structures where the barrier region is very thin, electronic coupling occurs in a time scale of hundreds of femtoseconds among the confined excited states. In a slightly longer time scale on the order of just a few picoseconds, electrons and holes relax from the high-lying states down to the low-lying dot states. When electrons and holes are captured non-geminately or separately into the excited states of different dots, the electrons experience a phonon bottleneck or the suppression of the interlevel relaxation. This bottleneck signal decays with a time constant of approximately 750 picoseconds and is attributed to thermal excitation. Temperature-dependent measurements analyzed with an ensemble Monte Carlo simulation indicate that thermal reemission and non-radiative recombination play a strong role in the carrier dynamics above 100 Kelvin. Collectively these results contribute to the ongoing efforts in the pursuit of a fuller understanding of the properties of self-assembled quantum dots.Ph.D.Applied SciencesCondensed matter physicsElectrical engineeringMaterials sciencePure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130721/2/3042184.pd