Hyeongrak Choi

Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities

We propose a photonic crystal nanocavity design with self-similar electromagnetic boundary conditions, achieving ultrasmall mode volume (V_{eff}). The electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions. We illustrate the design concept with a silicon-air one-dimensional photon crystal cavity that reaches an ultrasmall mode volume of V_{eff}∼7.01×10^{-5}λ^{3} at λ∼1550  nm. We show that the extreme light concentration in our design can enable ultrastrong Kerr nonlinearities, even at the single-photon level. These features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics.

A scalable multi-photon coincidence detector based on superconducting nanowires

Coincidence detection of single photons is crucial in numerous quantum technologies and usually requires multiple time-resolved single-photon detectors. However, the electronic readout becomes a major challenge when the measurement basis scales to large numbers of spatial modes. Here, we address this problem by introducing a two-terminal coincidence detector that enables scalable readout of an array of detector segments based on superconducting nanowire microstrip transmission line. Exploiting timing logic, we demonstrate a sixteen-element detector that resolves all 136 possible single-photon and two-photon coincidence events. We further explore the pulse shapes of the detector output and resolve up to four-photon events in a four-element device, giving the detector photon-number-resolving capability. This new detector architecture and operating scheme will be particularly useful for multi-photon coincidence detection in large-scale photonic integrated circuits.Superconducting nanowires can be engineered to realize scalable coincidence detectors of single photons.

Fast thermal relaxation in cavity-coupled graphene bolometers with a Johnson noise read-out

High sensitivity, fast response time and strong light absorption are the most important metrics for infrared sensing and imaging. The trade-off between these characteristics remains the primary challenge in bolometry. Graphene with its unique combination of a record small electronic heat capacity and a weak electron–phonon coupling has emerged as a sensitive bolometric medium that allows for high intrinsic bandwidths1–3. Moreover, the material’s light absorption can be enhanced to near unity by integration into photonic structures. Here, we introduce an integrated hot-electron bolometer based on Johnson noise readout of electrons in ultra-clean hexagonal-boron-nitride-encapsulated graphene, which is critically coupled to incident radiation through a photonic nanocavity with Q = 900. The device operates at telecom wavelengths and shows an enhanced bolometric response at charge neutrality. At 5 K, we obtain a noise equivalent power of about 10 pW Hz–1/2, a record fast thermal relaxation time, <35 ps, and an improved light absorption. However the device can operate even above 300 K with reduced sensitivity. We work out the performance mechanisms and limits of the graphene bolometer and give important insights towards the potential development of practical applications.A graphene–hBN heterostructure integrated onto a photonic crystal cavity shows enhanced bolometric response owing to improved light absorption and ultrafast thermal relaxation time.

Current status of antimonide-based mid-IR lasers

Summary form only given. Antimonide-based semiconductor lasers, either electrically or optically pumped, have made significant progress in the past few years. Near 2 /spl mu/m, GaInAsSb/AlGaAsSb quantum-well (QW) diode lasers have exhibited excellent performance, with room-temperature threshold current density as low as 50 A/cm/sup 2/, CW output power more than 1 W from 100-/spl mu/m aperture, and diffraction-limited CW power of 600 mW from tapered structures. Recently, room-temperature CW operation has been extended to 2.7 /spl mu/m by increasing the In content in GaInAsSb while limiting the As content to avoid the miscibility gap. The maximum CW power at 10/spl deg/C from a 100-/spl mu/m aperture was 500, 250 and 160 mW for 2.3, 2.5 and 2.6 /spl mu/m, respectively.

Wide-bandgap integrated photonic circuits for interfacing with quantum memories (Conference Presentation)

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 seminar, I will present results on ultraviolet wavelength operation, dispersion analysis, and propagation loss in aluminum nitride waveguides.

High-power optically pumped GaInSb/InAs quantum well lasers with GaInAsSb integrated absorber layers emitting at 4 /spl mu/m

Summary form only given. We believe we report the first demonstration of high-power GaInSb-InAs type-II QW lasers incorporating GaInAsSb absorber layers. To ensure good carrier transport from the absorber layers to the active wells, the absorber layers were inserted between each active well region.