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A variety of quantum degrees of freedom, e.g., spins, valleys, and localized emitters, in atomically thin van der Waals materials have been proposed for quantum information applications, and they inevitably couple to phonons. Here, we directly measure the intrinsic optical phonon decoherence in monolayer and bulk MoS2 by observing the temporal evolution of the spectral interference of Stokes photons generated by pairs of laser pulses. We find that a prominent optical phonon mode E2g exhibits a room-temperature dephasing time of ∼7 ps in both the monolayer and bulk. This dephasing time extends to ∼20 ps in the bulk crystal at ∼15 K, which is longer than previously thought possible. First-principles calculations suggest that optical phonons decay via two types of three-phonon processes, in which a pair of acoustic phonons with opposite momentum are generated.

Surface acoustic waves (SAWs) coupled to quantum dots (QDs), trapped atoms and ions, and point defects have been proposed as quantum transduction platforms, yet the requisite coupling rates and cavity lifetimes have not been experimentally established. Although the interaction mechanism varies, small acoustic cavities with large zero-point motion are required for high efficiencies. We experimentally establish the feasibility of this platform through electro- and opto-mechanical characterization of tightly focusing, single-mode Gaussian SAW cavities at $\sim$3.6 GHz on GaAs. We explore the performance limits of the platform by fabricating SAW cavities with mode volumes approaching 6$\lambda^3$ and linewidths $\leq$1 MHz. Employing strain-coupled single InAs QDs as optomechanical intermediaries, we measure single-phonon optomechanical coupling rates $g_0 \approx 2\pi \times 1.2$ MHz. Sideband scattering rates thus exceed intrinsic phonon loss, indicating the potential for quantum optical readout and transduction of cavity phonon states. To demonstrate the feasibility of this platform for low-noise ground-state quantum transduction, we develop a fiber-based confocal microscope in a dilution refrigerator and perform single-QD resonance fluorescence sideband spectroscopy at mK temperatures. These measurements show conversion between microwave phonons and optical photons with sub-natural linewidths., Comment: 15 pages, 10 figures

We demonstrate ~100-fold collection enhancements and strongly polarized emission from single InAs quantum dots in anisotropic semicircular dielectric grating optical cavities. In contrast to previous works, our cavities are on bulk substrates (i.e., not suspended).

We demonstrate coherent transduction of a frequency qubit from the microwave to optical domain by means of multimode surface acoustic wave cavities coupled to an InAs quantum dot.

We demonstrate modulation of the light scattered from a quantum emitter enhanced by surface acoustic wave cavities etched into the surface of GaAs, with the half-wave voltage V π as low as 44 mV.

A variety of quantum degrees of freedom, e.g., spins, valleys, and localized emitters, in atomically thin van der Waals materials have been proposed for quantum information applications, and they inevitably couple to phonons. Here, we directly measure the intrinsic optical phonon decoherence in monolayer and bulk MoS

Fast, efficient, and low-power modulation of light at microwave frequencies is crucial for chip-scale classical and quantum processing as well as for long-range networks of superconducting quantum processors. A successful approach to bridge the gap between microwave and optical photons has been to use intermediate platforms, such as acoustic waves, that couple efficiently to a variety of quantum systems. Here, we use gigahertz-frequency focusing surface acoustic wave cavities on GaAs that are piezo-electrically coupled to superconducting circuits and parametrically coupled, via strain, to photons scattered from InAs quantum dots. We demonstrate modulation of single photons with a half-wave voltage as low as 44 mV, and subnatural modulation sideband linewidths. These demonstrations pave the way for efficient and low-noise transduction of quantum information between microwave and optical domains.

We demonstrate etched-groove surface acoustic wave cavities on gallium arsenide with finesses reaching 100. These cavities can be used to enhance coupling between phonons and different quantum systems, providing a platform for quantum transduction.

We demonstrate modulation of scattered light from a quantum dot embedded in a surface acoustic wave cavity, and show coupling of red-detuned photons and the quantum dot mediated by phonons.

We investigate the exciton exchange interaction of erbium doped GaAs quantum well using MDCS. We observe an energy shift of ~100µeV consistent with the predicted exchange energy and different pulse sequences activate specific excitonic pathways.

We compare chiplet to monolithic quantum computing architectures using a network model that incorporates CX gate and link noise. As chiplets may have better internal gate fidelity, they may outperform monolithic architectures despite reduced connectivity.

We demonstrate focusing cavities of surface acoustic waves on gallium arsenide with quality factors reaching 20,000. These cavities can potentially enhance coupling of surface phonons to a wide variety of quantum systems, possibly enabling efficient quantum transduction.

Multidimensional coherent spectroscopy directly unravels multiply excited states that overlap in a linear spectrum. We report multidimensional coherent optical photocurrent spectroscopy in a semiconductor polariton diode and explore the excitation ladder of cavity polaritons. We measure doubly and triply avoided crossings for pairs and triplets of exciton polaritons, demonstrating the strong coupling between light and dressed doublet and triplet semiconductor excitations. These results demonstrate that multiply excited excitonic states strongly coupled to a microcavity can be described as two coupled quantum-anharmonic ladders.

In van der Waals (vdW) heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moire superlattice. While it is widely recognized that a moire superlattice can modulate the electronic band structure and lead to novel transport properties including unconventional superconductivity and insulating behavior driven by correlations, its influence on optical properties has not been investigated experimentally. We present spectroscopic evidence that interlayer excitons are confined by the moire potential in a high-quality MoSe2/WSe2 heterobilayer with small rotational twist. A series of interlayer exciton resonances with either positive or negative circularly polarized emission is observed in photoluminescence, consistent with multiple exciton states confined within the moire potential. The recombination dynamics and temperature dependence of these interlayer exciton resonances are consistent with this interpretation. These results demonstrate the feasibility of engineering artificial excitonic crystals using vdW heterostructures for nanophotonics and quantum information applications.

Improvements in temporal resolution of single-photon detectors enable increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging, and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the most efficient time-resolving single-photon-counting detectors available in the near-infrared, but understanding of the fundamental limits of timing resolution in these devices has been limited due to a lack of investigations into the timescales involved in the detection process. We introduce an experimental technique to probe the detection latency in SNSPDs and show that the key to achieving low timing jitter is the use of materials with low latency. By using a specialized niobium nitride SNSPD we demonstrate that the system temporal resolution can be as good as 2.6 ± 0.2 ps for visible wavelengths and 4.3 ± 0.2 ps at 1,550 nm. Knowledge about detection latency provides a guideline to reduce the timing jitter of niobium nitride superconducting nanowire single-photon detectors. A timing jitter of 2.6 ps at visible wavelength and 4.3 ps at 1,550 nm is achieved.

We demonstrate progress in developing a new microwave-optical quantum transducer. We demonstrate focusing and stable surface acoustic wave cavities at 3.4 GHz and characterize the acoustic performance. This work is a contribution of the National Institute of Standards and Technology; not subject to copyright in the United States of America.

We measure effect of strain on Auger recombination from compositional and applied biaxial stress using time-resolved photoluminescence and pump-probe spectroscopy. Results suggest that straining by composition, but not external stress, can tune the Auger coefficient.

We present a novel semiconductor single-photon source based on tensile-strained (111)-oriented GaAs/InAlAs quantum dots (QDs) exhibiting ultrasmall exciton fine-structure splitting (FSS) of ≤ 8 µeV. Using low-temperature micro-photoluminescence spectroscopy, we identify the biexciton-exciton radiative cascade from individual QDs, which, combined with small FSS, indicates these self-assembled GaAs(111) QDs are excellent candidates for polarization-entangled photon-pair generation.

We differentiate the effect of strain induced by lattice-mismatched growth from strain induced by mechanical deformation on cubic nonradiative Auger recombination in narrow-gap GaInAsSb/GaSb quantum well (QW) heterostructures. The typical reduction in the Auger coefficient observed with lattice-mismatched growth appears to be due to the concomitant compositional change rather than the addition of strain, with implications for mid-IR semiconductor laser design. We induced a range of internal compressive strain in five samples from −0.90% to −2.07% by varying the composition during the growth and mechanically induced a similar range of internal strain in analogous quantum well membrane samples. We performed time-resolved photoluminescence and differential reflectivity measurements to extract the carrier recombination dynamics, taken at 300 K with carrier densities from 2.7 × 10 18 cm−3 to 1.4 × 10 19 cm−3. We observed no change with strain in the cubic Auger coefficient of samples that were strained mechanically, but we did observe a trend with strain in samples that were strained by the QW alloy composition. Measured Auger coefficients ranged from 3.0 × 1 0 − 29 cm6 s−1 to 3.0 × 1 0 − 28 cm6 s−1.

In atomically thin two-dimensional semiconductors such as transition metal dichalcogenides (TMDs), controlling the density and type of defects promises to be an effective approach for engineering light-matter interactions. We demonstrate that electron-beam irradiation is a simple tool for selectively introducing defect-bound exciton states associated with chalcogen vacancies in TMDs. Our first-principles calculations and time-resolved spectroscopy measurements of monolayer ${\mathrm{WSe}}_{2}$ reveal that these defect-bound excitons exhibit exceptional optical properties including a recombination lifetime approaching 200 ns and a valley lifetime longer than $1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$. The ability to engineer the crystal lattice through electron irradiation provides a new approach for tailoring the optical response of TMDs for photonics, quantum optics, and valleytronics applications.

We present the fabrication and testing of photonic circuits using a III-V LED light source coupled to waveguide-integrated WSi single photon detectors for use in advanced computing and on-chip quantum optics experiments.

We demonstrate a new method for multidimensional coherent spectroscopy of nanostructures. We use a heterodyne technique implemented with a confocal microscope to record the amplitude and phase of all degenerate third-order wave-mixing processes.

We demonstrate cryogenic, electrically-injected, waveguide-coupled Si light-emitting diodes (LEDs) operating at 1.22 $\mu$m. The active region of the LED consists of W centers implanted in the intrinsic region of a $p$-$i$-$n$ diode. The LEDs are integrated on waveguides with superconducting nanowire single-photon detectors (SNSPDs). We demonstrate the scalability of this platform with an LED coupled to eleven SNSPDs in a single integrated photonic device. Such on-chip optical links may be useful for quantum information or neuromorphic computing applications.

We report on the optical gain and loss of waveguides containing lithographically defined quantum dots. Lasing action has previously been demonstrated in a nominally identical structure. Measurements are made by monitoring the transmission of a resonant pulse while varying the injection current. We measure a maximum modal gain of 1.8 cm \(^{{-1}}\) at the peak of the ground state emission for a two-layer structure. The peak gain is insufficient for ground state lasing to be achieved in a structure with as-cleaved facets, but the gain per dot is comparable with that demonstrated in self-assembled quantum dots.

We demonstrate cryogenic, all on-chip, single-photon-level photonic integrated circuits on a III-V platform with waveguide-coupled quantum-well sources and tungsten silicide superconducting nanowire single-photon detectors. We have measured the dark count rates below 10−3 counts/s and have reduced the cross talk to an adjacent waveguide by 30 dB.

Multidimensional coherent spectroscopy is a powerful tool for understanding the ultrafast dynamics of complex quantum systems. To fully characterize the nonlinear optical response of a system, multiple pulse sequences must be recorded and quantitatively compared. We present a new single-scan method that enables rapid and parallel acquisition of all unique pulse sequences corresponding to first- and third-order degenerate wave-mixing processes. Signals are recorded with shot-noise limited detection, enabling acquisition times of ∼2 minutes with ∼100 zs phase stability and ∼8 orders of dynamic range, in a collinear geometry, on a single-pixel detector. We demonstrate this method using quantum well excitons, and quantitative analysis reveals new insights into the bosonic nature of excitons. This scheme may enable rapid and scalable analysis of unique chemical signatures, metrology of optical susceptibilities, nonperturbative coherent control, and the implementation of quantum information protocols using multidimensional spectroscopy.

The detailed pathways of photoactivity on ultrafast time scales are a topic of contemporary interest. Using a tabletop apparatus based on a laser plasma X-ray source and an array of cryogenic microcalorimeter X-ray detectors, we measured a transient X-ray absorption spectrum during the ferrioxalate photoreduction reaction. With these high-efficiency detectors, we observe the Fe K edge move to lower energies and the amplitude of the extended X-ray absorption fine structure reduce, consistent with a photoreduction mechanism in which electron transfer precedes disassociation. These results are compared to previously published transient X-ray absorption measurements on the same reaction and found to be consistent with the results from Ogi et al. and inconsistent with the results of Chen et al. ( Ogi , Y. ; et al. Struct. Dyn. 2015 , 2 , 034901 ; Chen , J. ; Zhang , H. ; Tomov , I. V. ; Ding , X. ; Rentzepis , P. M. Chem. Phys. Lett. 2007 , 437 , 50 - 55 ). We provide quantitative limits on the Fe-O bond length change. Finally, we review potential improvements to our measurement technique, highlighting the future potential of tabletop X-ray science using microcalorimeter sensors.

We investigate phonon dephasing times in MoS 2 using a two-pulse coherent Raman spectroscopy method. The phonon dephasing times are 3.9 and 4.9 ps in monolayer and bulk MoS 2 at room temperature.

Experimental tools capable of monitoring both atomic and electronic structure on ultrafast (femtosecond to picosecond) time scales are needed for investigating photophysical processes fundamental to light harvesting, photocatalysis, energy and data storage, and optical display technologies. Time-resolved hard x-ray (>3 keV) spectroscopies have proven valuable for these measurements due to their elemental specificity and sensitivity to geometric and electronic structures. Here, we present the first tabletop apparatus capable of performing time-resolved x-ray emission spectroscopy. The time resolution of the apparatus is better than 6 ps. By combining a compact laser-driven plasma source with a highly efficient array of microcalorimeter x-ray detectors, we are able to observe photoinduced spin changes in an archetypal polypyridyl iron complex [Fe(2,2^{′}-bipyridine)_{3}]^{2+} and accurately measure the lifetime of the quintet spin state. Our results demonstrate that ultrafast hard x-ray emission spectroscopy is no longer confined to large facilities and now can be performed in conventional laboratories with 10 times better time resolution than at synchrotrons. Our results are enabled, in part, by a 100- to 1000-fold increase in x-ray collection efficiency compared to current techniques.

The intensity dynamics of a ve-emitter laser array subject to a linearly decreasing injection current are examined numerically. We have matched the results of the numerical model to an experi- mental AlGaAs quantum-dot array laser and have achieved the same robust oscillatory power output with a nearly phase shift between emitters that was observed in experiments. Due to the linearly decreas- ing injection current, the output power of the waveg- uide decreases as a function of waveguide number. For injection currents ranging from 380 to 500 mA, the oscillatory behavior persists with only a slight change in phase dierence. However, the fundamental fre- quency of oscillation increases with injection current, and higher harmonics as well as some ve-element array operating in the oscillatory regime with an uneven injection current. The application of Winful's model to such a device produces results which are consistent with experimental results from an AlGaAs quantum-dot array operating in the same regime. Of particular interest is the frequency of oscillation, as a potential uses of this sort of array is as an all-optical GHz oscillator for pho- tonic integrated circuits. The model of the array dynamics involves the coupling of the optical eld to the carrier density dynamics. This model is derived from a simplication of Maxwell's wave equation where a TE mode, the slowly varying envelope

We report lasing wavelength bistability with respect to applied bias on the saturable absorbers in two-section mode-locked quantum dot lasers. We show data from three different devices exhibiting wavelength bistability. All lasers display wavelength bistability. Only one lasing wavelength is present at a time, with all other wavelengths totally quenched. The switchable ranges (the wavelength difference between two bistable lasing branches) are different for all three lasers and in one device can be manipulated by changing the current injection. All lasers show the remarkable property of switching only in integer multiples of about 8 nm. The bistable operation can be explained by the interplay of the cross-saturation and self-saturation properties in gain and absorber, and the quantum-confined Stark effect in absorber. The measured switching time between bistable wavelengths is 150 ps.

Micropillar devices have shown promise as single photon sources for applications in quantum key distribution as well as single photon metrology and fundamental science. For higher temperature operation (77K), a high quality factor (Q) cavity and a small modal volume are necessary for enhanced spontaneous emission. Although high Q’s have been demonstrated, achieving small modal volumes is difficult due to the limited index contrast available from the lattice-matched Bragg layers of GaAs and AlGaAs. However, by wet thermal oxidation of AlGaAs or AlAs layers to amorphous aluminum oxide (AlOx), very high index contrast layers can be obtained. This allows for high reflectivity mirrors with fewer Bragg pairs, resulting in reduced mode volume from reduced penetration of the optical mode within the mirror pairs. The authors apply this method in a GaAs∕Al0.95Ga0.05As material system and describe a fabrication process for such devices, utilizing a BCl3:Cl2:Ar etch. Photoluminescence measurements of micropillars wit...

We demonstrate a device that integrates a III-V semiconductor saturable absorber mirror with a graphene electro-optic modulator, which provides a monolithic solution to modelocking and noise suppression in a frequency comb. The device offers a pure loss modulation bandwidth exceeding 5 MHz and only requires a low voltage driver. This hybrid device provides not only compactness and simplicity in laser cavity design, but also small insertion loss, compared to the previous metallic-mirror-based modulators. We believe this work paves the way to portable and fieldable phase-coherent frequency combs.

Minimizing decoherence due to coupling of a quantum system to its fluctuating environment is at the forefront of quantum information and photonics research. Nature sets the ultimate limit, however, given by the strength of the system's coupling to the electromagnetic field. Here, we establish the ability to electronically control this coupling and enhance the optical coherence time of the charged exciton transition in quantum dots embedded in a photonic waveguide. By manipulating the electronic wave functions through an applied lateral electric field, we increase the coherence time from $\ensuremath{\sim}1.4$ to $\ensuremath{\sim}2.7\text{ }\text{ }\mathrm{ns}$. Numerical calculations reveal that longer coherence arises from the separation of charge carriers by up to $\ensuremath{\sim}6\text{ }\text{ }\mathrm{nm}$, which leads to a 30% weaker transition dipole moment. The ability to electronically control the coherence time opens new avenues for quantum communication and novel coupling schemes between distant qubits.

We present x-ray absorption and emission measurements of Fe-based compounds using ionizing radiation generated by a femtosecond pulsed laser source in combination with superconducting microcalorimeters.

We report development of two absorption-based spectroscopic methods that have been adapted from atomic physics techniques to elucidate the basic physical properties of InGaAs/GaAs self-assembled quantum dots(SAQDs). Absorptive spectroscopic measurements allow the examination of the SAQDs optical transitions free from carrier relaxation effects. In addition, we employ these techniques to study SAQDs' optical transition with a level of spectral resolution not available using ultra-fast techniques. The first of the two approaches we discuss is cavity ring-down spectroscopy (CRDS), which permits an absolute measurement of absorption. We report on initial application of CRDS to SAQDs and present an assessment based on these measurements for single SAQD spectroscopy using this technique. The second method, spectral hole burning, is applied to SAQDs in a semiconductor ridge waveguide and permits the homogeneous linewidth of the SAQDs to be separated from the broad inhomogeneous spectrum.

We demonstrate a device that integrates a III-V semiconductor saturable absorber mirror with a graphene electro-optic modulator, which provides a monolithic solution to modelocking and noise suppression in a frequency comb.

Differential transmission spectroscopy of InAs QDs reveals that the positively charged exciton homogeneous linewidth is broadened by the electron hyperfine interaction. Application of a Faraday magnetic field screens the interaction, narrowing the linewidth by 25%.

In semiconductor quantum dots, the electron hyperfine interaction with the nuclear spin bath is the leading source of spin decoherence at cryogenic temperature. Using high-resolution two-color differential transmission spectroscopy, we demonstrate that such electron-nuclear coupling also imposes a lower limit for the positively charged exciton dephasing rate, \gamma, in an ensemble of InAs/GaAs quantum dots. We find that the dephasing rate is sensitive to the strength of the hyperfine interaction, which can be controlled through the application of an external magnetic field in the Faraday configuration. At zero applied field, strong electron-nuclear coupling induces additional dephasing beyond the radiative limit and \gamma = 230 MHz (0.95 \mu eV). Screening of the hyperfine interaction is achieved for an external field of ~1 T, resulting in \gamma = 172 MHz (0.71 \mu eV) limited only by spontaneous recombination. On the other hand, application of a Voigt magnetic field mixes the spin eigenstates, which increases the dephasing rate by up to 75%. These results are reproduced with a simple and intuitive model that captures the essential features of the electron hyperfine interaction and its influence on \gamma., Comment: 9 pages, 6 figures

We report the development of high quality, broad-bandwidth, antireflection (AR) coatings using the low index provided by wet thermally oxidized Al0.98Ga0.02As. We address the design criteria, fabrication, and characterizations of AR coatings composed of surface and buried oxide layers on GaAs. We show, using native-oxide dispersion data, that surface oxide coatings can be designed to offer a nearly zero minimum of reflectance and a reflectance of 250 nm have been experimentally demonstrated at a design wavelength of 1 micrometer. Additionally, buried oxide coatings can be designed with an AlxGa1−xAs matching layer of any composition to exactly match the admittance of any substrate with effective index between 2.5 and 3.5. We have demonstrated buried oxide coatings, also designed for 1 micrometer, having a reflectance minimum of 0.4% and a reflectance of

We report a two-section mode-locked quantum-dot laser with an emission wavelength that is bistable with respect to applied bias on the saturable absorber region. The two stable lasing wavelengths for this device are about 1173 and 1166 nm with a power contrast ratio of over 30 dB. The largest switchable wavelength range is 7.7 nm. The optical power and pulsewidth (6.5ps) are almost identical in the two lasing modes under optimized conditions. The operation of this laser can be explained by the interplay of the spectral-hole burning and the quantum-confined Stark effect

We present a new technique for Multi-Dimensional Coherent spectroscopy of nano-structures. We measure the Four-Wave Mixing (FWM) amplitude and phase via photocurrent detection. The measurement is suitable for any nano-structures that can be electrically contacted.

Multidimensional Coherent Optical Photocurrent Spectroscopy (MD-COPS) is implemented using unstabilized interferometers. Photocurrent from a semiconductor sample is generated using a sequence of four excitation pulses in a collinear geometry. Each pulse is frequency shifted by a unique radio frequency through acousto-optical modulation; the Four-Wave Mixing (FWM) signal is then selected in the frequency domain. The interference of an auxiliary continuous wave laser, which is sent through the same interferometers as the excitation pulses, is used to synthesize reference frequencies for lock-in detection of the photocurrent FWM signal. This scheme enables the partial compensation of mechanical fluctuations in the setup, achieving sufficient phase stability without the need for active stabilization. The method intrinsically provides both the real and imaginary parts of the FWM signal as a function of inter-pulse delays. This signal is subsequently Fourier transformed to create a multi-dimensional spectrum. Measurements made on the excitonic resonance in a double InGaAs quantum well embedded in a p-i-n diode demonstrate the technique.

We present time-resolved X-ray absorption measurements of vanadium dioxide using ionizations radiation generated by a femtosecond pulsed laser source in combination with superconducting microcalorimeters capable of measuring energies of individual radiation quanta.

We directly measure the optical gain and threshold current of lithographically-defined quantum dots. A peak groundstate gain of 1.8 cm−1 is determined. We also measure the recovery dynamics of the groundstate with the device biased above and below transparency using ultrafast differential transmission spectroscopy.