Quantum information processing relies on the fundamental property of quantum interference, where the quality of the interference directly correlates to the indistinguishability of the interacting particles. The creation of these indistinguishable particles, photons in this case, has conventionally been accomplished with nonlinear crystals and optical filters to remove spectral distinguishability, albeit sacrificing the number of photons. This research describes the use of an integrated aluminum nitride microring resonator circuit to selectively generate photon pairs at the narrow cavity transmissions, thereby producing spectrally indistinguishable photons in the ultraviolet regime to interact with trapped ion quantum memories. The spectral characteristics of these photons must be carefully controlled for two reasons: (i) interference quality depends on the spectral indistinguishability, and (ii) the wavelength must be strictly controlled to interact with atomic transitions. The specific ion of interest for these trapped ion quantum memories is Ytterbium which has a transition at 369.5 nm with 12.5 GHz offset levels. Ytterbium ions serve as very long lived and stable quantum memories with storage times on the order of 10’s of minutes, compared with photonic quantum memories which are limited to 10-6 to 10-3 seconds. The combination of the long lived atomic memory, integrated photonic circuitry, and the photonic quantum bits are necessary to produce the first quantum information processors. In this article, I will present results on wavelength operation, dispersion analysis, and second harmonic generation in aluminum nitride waveguides.
Two-dimensional (2-D) materials are of tremendous interest to silicon photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here we present a new route for 2-D material integration with silicon photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides achieving improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators based on graphene and black phosphorus.
Ring resonators are used as photon pair sources by taking advantage of the materials second or third order non- linearities through the processes of spontaneous parametric downconversion and spontaneous four wave mixing respectively. Two materials of interest for these applications are silicon for the infrared and aluminum nitride for the ultraviolet through the infrared. When fabricated into ring type sources they are capable of producing pairs of indistinguishable photons but typically suffer from an effective 50% loss. By slightly decoupling the input waveguide from the ring, the drop port coincidence ratio can be significantly increased with the trade-off being that the pump is less efficiently coupled into the ring. Ring resonators with this design have been demonstrated having coincidence ratios of 96% but requiring a factor of ~10 increase in the pump power. Through the modification of the coupling design that relies on additional spectral dependence, it is possible to achieve similar coincidence ratios without the increased pumping requirement. This can be achieved by coupling the input waveguide to the ring multiple times, thus creating a Mach-Zehnder interferometer. This coupler design can be used on both sides of the ring resonator so that resonances supported by one of the couplers are suppressed by the other. This is the ideal configuration for a photon-pair source as it can only support the pump photons at the input side while only allowing the generated photons to leave through the output side. Recently, this device has been realized with preliminary results exhibiting the desired spectral dependence and with a coincidence ratio as high as ~ 97% while allowing the pump to be nearly critically coupled to the ring. The demonstrated near unity coincidence ratio infers a near maximal heralding efficiency from the fabricated device. This device has the potential to greatly improve the scalability and performance of quantum computing and communication systems.
Ultrafast electrically driven light emitter is a critical component in the development of the high bandwidth free-space and on-chip optical communications. Traditional semiconductor based light sources for integration to photonic platform have therefore been heavily studied over the past decades. However, there are still challenges such as absence of monolithic on-chip light sources with high bandwidth density, large-scale integration, low-cost, small foot print, and complementary metal-oxide-semiconductor (CMOS) technology compatibility. Here, we demonstrate the first electrically driven ultrafast graphene light emitter that operate up to 10 GHz bandwidth and broadband range (400 ~ 1600 nm), which are possible due to the strong coupling of charge carriers in graphene and surface optical phonons in hBN allow the ultrafast energy and heat transfer. In addition, incorporation of atomically thin hexagonal boron nitride (hBN) encapsulation layers enable the stable and practical high performance even under the ambient condition. Therefore, electrically driven ultrafast graphene light emitters paves the way towards the realization of ultrahigh bandwidth density photonic integrated circuits and efficient optical communications networks.
Bio-imaging requires robust ultra-bright probes without causing any toxicity to the cellular environment, maintain their
stability and are chemically inert. In this work we present hexagonal boron nitride (hBN) nanoflakes which exhibit
narrowband ultra-bright single photon emitters1. The emitters are optically stable at room temperature and under ambient
environment. hBN has also been noted to be noncytotoxic and seen significant advances in functionalization with
biomolecules2,3. We further demonstrate two methods of engineering this new range of extremely robust multicolour
emitters across the visible and near infrared spectral ranges for large scale sensing and biolabeling applications.
Quantum information processing relies on the fundamental property of quantum interference, where the quality of the interference directly correlates to the indistinguishability of the interacting particles. The creation of these indistinguishable particles, photons in this case, has conventionally been accomplished with nonlinear crystals and optical filters to remove spectral distinguishability, albeit sacrificing the number of photons. This research describes the use of an integrated aluminum nitride microring resonator circuit to selectively generate photon pairs at the narrow cavity transmissions, thereby producing spectrally indistinguishable photons. These spectrally indistinguishable photons can then be routed through optical waveguide circuitry, concatenated interferometers, to manipulate and entangle the photons into the desired quantum states. Photon sources and circuitry are only two of the three required pieces of the puzzle. The final piece which this research is aimed at interfacing with are trapped ion quantum memories, based on trapped Ytterbium ions. These ions serve as very long lived and stable quantum memories with storage times on the order of 10’s of minutes, compared with photonic quantum memories which are limited to 10-6 to 10-3 seconds. The caveat with trapped ions is the interaction wavelength of the photons is 369.5nm and therefore the goal of this research is to develop entangled photon sources and circuitry in that wavelength regime to interact directly with the trapped ions and bypass the need for frequency conversion.
The negatively charged nitrogen vacancy (NV) center in diamond is a promising solid-state quantum memory. However, developing networks comprising such quantum memories is limited by the fabrication yield of the quantum nodes and the collection efficiency of indistinguishable photons. In this letter, we report on advances on a hybrid quantum system that allows for scalable production of networks, even with low-yield node fabrication. Moreover, an NV center in a simple single mode diamond waveguide is shown in simulation and experiment to couple well to a single mode SiN waveguide with a simple adiabatic taper for optimal mode transfer. In addition, cavity enhancement of the zero phonon line of the NV center with a resonance coupled to the waveguide mode allows a simulated <1800 fold increase in the collection of photon states coherent with the state of the NV center into a single frequency and spatial mode.
A central goal of quantum information science is the entanglement of multiple quantum memories that can be individually controlled. Here, we discuss progress towards photonic integrated circuits designed to enable efficient optical interactions between multiple spin qubits in nitrogen vacancy (NV) centers in diamond. We describe NV-nanocavity systems in the strong Purcell regime with optical quality factors approaching 10,000 and electron spin coherence times exceeding 200 μs; implantation of NVs with nanometer-scale apertures, including into cavity field maxima; hybrid on-chip networks for integration of multiple functional NV-cavity systems; and scalable integration of superconducting nanowire single photon detectors on-chip.
There has been a rapidly growing interest in graphene-based optoelectronics. This exceptional material exhibits broadband optical response, ultrahigh carrier mobility and more importantly, potential compatibility with silicon complementary metal-oxide semiconductor (CMOS) technology. Here we present our recent works that integrate graphene with silicon channel waveguides and photonic crystal cavities. By coupling graphene to an optical cavity, we demonstrated an efficient electro-optic modulator that features a modulation depth of 10 dB and a switching energy of 300 fJ. Several high-speed modulators are also tested, showing a speed up to 0.57 GHz. In addition, we implemented a graphene photodetector on a silicon waveguide. The 53-μm-long graphene channel couples to the evanescent field of the waveguide mode, resulting in more than 60% absorption of the input light. We demonstrated a responsivity of 0.108 A/W in our photodetector. A data transmission of 12 Gbps and response time in excess of 20 GHz are also achieved. These results show the feasibility of graphene as a building block for silicon photonic integrated circuits. In particular, on-chip graphene active devices such as modulators and photodetectors are promising for their broadband response, high-speed operation, low power consumption and ease-to-fabrication.
We study the dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. We demonstrate switching between two weak pulsed beams (40 ps pulses), observing an increase of the systems transmission when the signal and the control pulses overlap inside the cavity. Our results show that the quantum dot-nanocavity system enables fast, controllable optical switching at the single-photon level.
Optical nanocavities enable a strong interaction between single photons and single emitters. An appealing
application is the construction of a quantum interface for photonic and solid state qubits. Since the material of
the solid state qubit is often dierent from the nanocavity, there has been considerable interest in combining the
two in a hybrid architecture. We describe our recent development of such a hybrid interface based a Gallium
Phosphide photonic crystal nanocavity that is scanned and deterministically coupled to single emitters on a
surface. The technique is used to couple the cavity to the nitrogen vacancy center in diamond, an emitter system
with optically accessible electron spins and the ability to transfer electronic spin states to nuclear spins.
Single InAs quantum dots can be used to control the transmission function of photonic crystal cavities, as we
have already shown for systems that operate both in strong and weak coupling regime. Here we present our most
recent work on devices where the cavity is connected in a micron-scale optical network via multiple photonic
crystal waveguides terminated with input and output optical couplers. This architecture allows for multiple
signal and control beams to be coupled simultaneously in the cavity via distinct ports. The devices are equipped
with two input ports where the waveguides are terminated with input grating-couplers that allow for coupling
into the waveguide from an out-of-plane direction. A third waveguide coupled to the cavity is terminated with
a different kind of grating out-coupler that allows for improved directional scattering of the light transmitted
through the cavity. We have already shown in previous experiments with a single cavity with coupled quantum
dots, that this system acts as a highly nonlinear medium that enables all optical switching at powers down to
the single photon level. In our most recent experiments we take significant steps towards demonstrating that this
switching can be done in integrated structures, as needed for optical signal processing devices for both classical
and quantum information science.
In this paper, we review some recent cavity quantum electrodynamic (CQED) experiments with single quantum
dot exciton coupled to photonic crystal cavities, performed in our group. We show how the coupled quantum-dot/
cavity system can be used to modulate light with at a very fundamental level with very low power and
discuss some applications of these low power modulators.
A quantum dot strongly coupled to a photonic crystal resonator is used to investigate cavity quantum electro-
dynamics phenomena in solid state physics. Nonlinear optical phenomena such as photon blockade and photon
induced tunneling are observed in this system. The nonlinearity of this system is sensitive to intra-cavity photon
numbers close to unity, and it has been used to demonstrate conditional phase shifts of 28° at a single photon
level and a second order auto-correlation of g2(0) = 0.9 in the photon blockade regime.
The strong coupling regime between a single emitter and the mode of an optical resonator allows for nonlinear
optics phenomena at extremely low light intensities. Down to the single photon level, extreme nonlinearities can
be observed, where the presence of a single photon inside the resonator either blocks or enhances the probability
of subsequent photons entering the resonator. In this paper we experimentally show the existence of these
phenomena, named photon blockade and photon induced tunneling, in a solid state system composed of a
photonic crystal cavity with a strongly coupled quantum dot.
We coherently probe a quantum dot that is strongly coupled to a photonic crystal nano-cavity by scattering of a resonant laser beam.
The coupled system's response is highly nonlinear as the quantum dot saturates with nearly one photon per cavity lifetime. This system
enables large amplitude and phase shifts of a signal beam via a control beam, both at single photon levels. We demonstrate photon-photon
interactions with short pulses in a system that is promising for ultra-low power switches and two-qubit quantum gates.
We discuss recent our recent progress on functional photonic crystals devices and circuits for classical and quantum
information processing. For classical applications, we have demonstrated a room-temperature-operated, low
threshold, nanocavity laser with pulse width in the picosecond regime; and an all-optical switch controlled with
60 fJ pulses that shows switching time on the order of tens of picoseconds. For quantum information processing,
we discuss the promise of quantum networks on multifunctional photonic crystals chips. We also discuss a new
coherent probing technique of quantum dots coupled to photonic crystal nanocavities and demonstrate amplitude
and phase nonlinearities realized with control beams at the single photon level.
We have recently demonstrated an ultrafast photonic crystal laser and cavity coupled laser array with modulation
rates of 1THz at room temperature, a 20 GHz optical modulator with activation energies of 60 fJ and a quantum
dot photonic crystal laser with large signal modulation rates of 30GHz. These devices are enabled by the
enhanced light-matter interaction in photonic crystals, and serve as the building blocks of on-optical information
We have recently developed a technique for local, reversible tuning of individual quantum dots on a photonic
crystal chip by up to 1.8nm, which overcomes the problem of large quantum dot inhomogeneous broadening -
usually considered the main obstacle in employing such platform in practical quantum information processing
systems. We have then used this technique to tune single quantum dots into strong coupling with a photonic
crystal cavity, and observed strong coupling both in photoluminescence and in resonant light scattering from the
system, as needed for several proposals for scalable quantum information networks and quantum computation.
We have recently demonstrated a number of functional photonic crystals devices and circuits, including an ultrafast, roomtemperature,
low threshold, nanocavity laser with the direct modulation speed approaching 1THz, an all-optical switch
controlled with 60 fJ pulses and with the speed exceeding 20GHz, and a local, reversible tuning of individual quantum dots
on a photonic crystal chip by up to 1.8nm, which was then used to tune single quantum dots into strong coupling with a
photonic crystal cavity and to achieve a giant optical nonlinearity.
We demonstrate the coupling of PbS quantum dot emission to photonic crystal cavities at room temperature. The cavities are defined in 33% Al, AlGaAs membranes on top of oxidized AlAs. Quantum dots were dissolved in Poly-methyl-methacrylate (PMMA) and spun on top of the cavities. Quantum dot emission is shown to map out the structure resonances, and may prove to be viable sources for room temperature cavity coupled single photon generation for quantum information processing applications. These results also indicate that such commercially available quantum dots can be used for passive structure characterization. The deposition technique is versatile and allows layers with different dot densities and emission wavelengths to be re-deposited on the same chip.
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