The use of a high-contrast grating (HCG) as the top mirror in a vertical-cavity surface-emitting laser (VCSEL) allows for setting the resonance wavelength by the grating parameters in a post-epitaxial growth fabrication process. Using this technique, we demonstrate electrically driven multi-wavelength VCSEL arrays at ~980 nm wavelength. The VCSELs are GaAs-based and the suspended GaAs HCGs were fabricated using electron-beam lithography, dry etching and selective removal of an InGaP sacrificial layer. The air-coupled cavity design enabled 4-channel arrays with 5 nm wavelength spacing and sub-mA threshold currents thanks to the high HCG reflectance.
We present DWDM nanophotonics architectures based on microring resonator modulators and detectors. We
focus on two implementations: an on chip interconnect for multicore processor (Corona) and a high radix network
switch (HyperX). Based on the requirements of these applications we discuss the key constraints on the photonic
circuits' devices and fabrication techniques as well as strategies to improve their performance.
We report a numerical study on the frequency property of a system composed of an optical antenna array placed on the
surface of a dielectric grating. Such a periodic structure is designed for Raman spectroscopy application because of its
advantages over the conventional rough-surface based surface enhanced Raman spectroscopy: the position of the high
field intensity and the exact field magnitude is well controlled by the design, and the constructive interference from the
elements placed in periodic array may form a collective resonance and provide a further enhancement to the field
intensity. By integrating and weakly coupling the guided mode resonance (GMR) of a dielectric grating with optical
nano-antennas made of plasmonic materials that are also field-enhancing devices, it provides a further enhanced local
field around the antenna. We specifically studied the behavior of the device under oblique incidence, and show that
multiple resonant peaks are observed in the spectrum. The application of the device in a Raman process is discussed in
We present a novel quantum communication protocol for "Private Data Sampling", where a player (Bob) obtains
a random sample of limited size of a classical database, while the database owner (Alice) remains oblivious as
to which bits were accessed. The protocol is efficient in the sense that the communication complexity per query
scales at most linearly with the size of the database. It does not violate Lo's "no-go" theorem for one-sided twoparty
secure computation, since a given joint input by Alice and Bob can result in randomly different protocol
outcomes. After outlining the main security features of the protocol, we present our first experimental results.
High-channel-count WDM will eventually be used for short reach optical interconnects since it maximizes link bandwidth and efficiency. An impediment to adoption is the fact that each WDM wavelength currently requires its own DFB laser. The alternative is a single, multi-wavelength laser, but noise, size and/or expense make existing options impractical. In contrast, a new low-noise, diode comb laser based on InAs/GaAs quantum dots provides a practical and timely alternative, albeit in the O-band. Samples are being evaluated in short reach WDM development systems. Tests show this type of Fabry-Perot laser permits >10 Gb/s error-free modulation of 10 to over 50 separate channels, as well as potential for 1.25 Gb/s direct modulation. The paper describes comb laser requirements, noise measurements for external and direct modulation, O-band issues, transmitter photonic circuitry and components, future CMP applications, and optical couplers that may help drive down packaging costs to below a dollar.
We present an unconditionally secure Oblivious Transfer protocol relying on two rounds of entanglement-free
quantum communication. When played honestly, the protocol only requires the ability to measure a single qubit
in a fixed basis, and to perform a coherent bit-flip (Pauli X) operation. We present a generalization to a "Private
Data Sampling" protocol, where a player (Bob) can obtain a random sample of fixed size from a classical database
of size N, while the database owner (Alice) remains oblivious as to which bits were accessed. The protocol is
efficient in the sense that the communication complexity per query scales at most linearly with the size of the
database. It does not violate Lo's "no-go" theorem for one-sided two-party secure computation, since a given
joint input by Alice and Bob can result in randomly different protocol outcomes. Finally it could be used to
implement a practical bit string commitment protocol, among other applications.
Nanophotonic structures can be used to dramatically enhance interactions between light and matter. We describe some of
our recent progress in fabricating optical nanostructures suitable for both classical and quantum information processing.
In particular, we present our progress using nanoimprint lithography, a low cost nanoreplication method, to fabricate low
loss photonic crystals.
General requirements for single-photon devices in various applications are presented and compared with experimental
progress to date. The quantum information applications that currently appear the most promising require
a matter qubit-enabled single-photon source, where the emitted photon state is linked to the state of a long-lived
quantum system such as an electron spin. The nitrogen-vacancy center in diamond is a promising solid-state
system for realizing such a device due to its long-lived electron spin coherence, optical addressability, and ability
to couple to a manageable number of nuclear spins. This system is discussed in detail, and experimental results
from our laboratory are shown. A critical component of such a device is an optical microcavity to enhance the
coupling between the nitrogen-vacancy center and a single photon, and we discuss theoretically the requirements
for achieving this enhancement.
We propose a novel design for a guided-mode resonance (GMR) grating sensor that extends the sensitivity to a
large region of space, possibly several tens of microns away from the grating surface. This type of sensors has
high sensitivity in the half-space above the grating, close to the theoretical limit, together with a controllable -
potentially very high - quality factor. It relies on a resonance caused by a "confined" mode of a sub-wavelength
thick grating slab, a mode that is largely expelled from the grating itself into the grating environment. The small
thickness assumption allows us to derive a simple yet accurate analytical model for the sensor behavior, which
is tested numerically using a rigorous coupled-wave analysis (RCWA) method as well as in preliminary grating
We propose a novel design for a guided-mode resonance (GMR) grating sensor that is optimized for detecting
small average index changes in an extended region of space, retaining sensitivity up to several tens of microns
away from the grating surface at optical detection frequencies. This kind of sensors has high sensitivity in the
half-space above the grating, close to the theoretical limit, together with a controllable - potentially very high - quality factor. It relies on a resonance with a "confined" mode of a sub-wavelength thick grating slab, a mode
that is largely expelled from the grating itself. The small thickness assumption allows us to derive analytical
expressions for many properties of these sensors, expressions that are then tested numerically using a rigorous
coupled-wave analysis (RCWA) method, and in preliminary experiments.
Nitrogen-vacancy centers in diamond typically have spin-conserving optical transitions, a feature which allows
for optical detection of the long-lived electronic spin states through fluorescence detection. However, by applying
stress to a sample it is possible to obtain spin-nonconserving transitions in which a single excited state couples to
multiple ground states. Here we describe two-frequency optical spectroscopy on single nitrogen-vacancy centers
in a high-purity diamond sample at low temperature. When stress is applied to the sample it is possible to
observe coherent population trapping with a single center. By adjusting the stress it is possible to obtain a
situation in which all of the transitions from the three ground sublevels to a common excited state are strongly
allowed. These results show that all-optical spin manipulation is possible for this system, and we propose that
that by coupling single centers to optical microcavities, a scalable quantum network could be realized for photonic
quantum information processing.
Moore's Law has set great expectations that the performance/price ratio of commercially available semiconductor
devices will continue to improve exponentially at least until the end of the next decade. Although the physics
of nanoscale silicon transistors alone would allow these expectations to be met, the physics of the metal wires
that connect these transistors will soon place stringent limits on the performance of integrated circuits. We
will describe a Si-compatible global interconnect architecture - based on chip-scale optical wavelength division
multiplexing - that could precipitate an "optical Moore's Law" and allow exponential performance gains until
the transistors themselves become the bottleneck. Based on similar fabrication techniques and technologies, we
will also present an approach to an optically-coupled quantum information processor for computation beyond
Moore's Law, encouraging the development of practical applications of quantum information technology for
commercial utilization. We present recent results demonstrating coherent population trapping in single N-V
diamond color centers as an important first step in this direction.
We report on two experiments implementing quantum communications primitives in linear optics systems: a
secure Quantum Random Bit Generator (QRBG) and a multi-qubit gate based on Two-Photon Multiple-Qubit
(TPMQ) quantum logic. In the first we use photons to generate random numbers and introduce and implement
a physics-based estimation of the sequence randomness as opposed to the commonly used statistical tests. This
scheme allows one to detect and neutralize attempts to eavesdrop or influence the random number sequence. We
also demonstrate a C-SWAP gate that can be used to implement quantum signature and fingerprinting protocols.
A source of momentum-entangled photons, remote state preparation, and a C-SWAP gate are the ingredients
used for this proof-of-principle experiment. While this implementation cannot be used in field applications due to the limitations of TPMQ logic, it provides useful insights into this protocol.
We describe how a quantum non-demolition device based on electromagnetically-induced transparency in solidstate atom-like systems could be realized. Such a resource, requiring only weak optical nonlinearities, could potentially enable photonic quantum information processing (QIP) that is much more efficient than QIP based on linear optics alone. As an example, we show how a parity gate could be constructed. A particularly interesting physical system for constructing devices is the nitrogen-vacancy defect in diamond, but the excited-state structure for this system is unclear in the existing literature. We include some of our latest spectroscopic results that indicate that the optical transitions are generally not spin-preserving, even at zero magnetic field, which allows the realization of a Λ-type system.
We report on single photon sources produced from photonic crystal - coupled InAs Quantum Dots (QDs). We observe large spontaneous emission rate modification of individual InAs Quantum Dots (QDs) in modified single defect cavities with large quality factor (Q). Compared to QDs in bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase by up to a factor of 8. In contrast, off-resonant QDs indicate up to five-fold rate quenching as the local density of optical states (LDOS) is diminished in the photonic crystal. In both cases we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using Finite Difference Time Domain (FDTD) simulations and find good agreement with experiment. High multiphoton suppression is achieved by resonant excitation. Finally, we discuss fabrication improvements based on FDTD analysis of already fabricated structures.
We describe our work on development of high efficiency single photon sources based on the interaction of InAs quantum dots with a photonic crystal micro-cavity. Sub-poisson statistics and lifetime modifications are experimentally demonstrated. We then investigate improvement of the source using coupling to a photonic crystal waveguide for easy collection. We analyze the system using coupled mode theory, and infer the parameters needed to create good coupling efficiency.
Single-photon sources rarely emit two or more photons in the same
pulse, compared to a Poisson-distributed source of the same
intensity, and have numerous applications in quantum information
science. The quality of such a source is evaluated based on three
criteria: high efficiency, small multi-photon probability, and
quantum indistinguishability. We have demonstrated a single-photon
source based on a quantum dot in a micropost microcavity that
exhibits a large Purcell factor together with a small multi-photon
probability. For a quantum dot on resonance with the cavity, the
spontaneous emission rate has been increased by a factor of five,
while the probability to emit two or more photons in the same
pulse has been reduced to 2% compared to a Poisson-distributed
source of the same intensity. The indistinguishability of emitted
single photons from one of our devices has been tested through a
Hong-Ou-Mandel-type two-photon interference experiment;
consecutive photons emitted from such a source have been largely
indistinguishable, with a mean wave-packet overlap as large as
0.81. We have also designed and demonstrated two-dimensional
photonic crystal GaAs cavities containing InAs quantum dots that
exhibit much higher quality factors together with much smaller
mode volumes than microposts, and therefore present an ideal
platform for construction of single photon sources of even higher
Quantum cryptography is a method to exchange secret messages with unconditional security over a potentially hostile environment using single photons. Previous implementations of quantum cryptography have relied on highly attenuated laser light to approximate single photo states. Such sources are vulnerable to eavesdropping attacks based on photon splitting. Here we present an experimental demonstration of quantum cryptography using a single photon source based on Indium Arsenide quantum dots. We achieve a communication rate of 25kbits/s. This source allows secure communication over a quantum channel with up to 28dB of channel loss, as opposed to only 23dB for an attenuated laser.
A high efficiency, triggered single photon source with applications to quantum communications is discussed. The sources is formed from an InAs-based quantum dot located in the center of a micropost cavity formed from GaAs, with top and bottom GaAs/AlAs distributive Bragg reflector pairs, and lateral processing. When pumped above band into the semiconductor host, correlation measurements show a reduction in the two-photon probability to 0.14, compared to unity for a Poisson source. The external efficiency of this structure is 0.24.
A single-photon device based on a semiconductor quantum dot
embedded in an optical microcavity is described. The spontaneous
emission lifetime, multi-photon suppression, and spectral linewidth
are measured. It is then shown that consecutively emitted photons possess a large degree of quantum-mechanical indistinguishability, with a mean wave-packet overlap as large as 0.8. This demonstration is accomplished through a Hong-Ou-Mandel-type two-photon interference experiment.