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1. Fast phase cycling in non-collinear optical two-dimensional coherent spectroscopy

   https://doi.org/10.1364/OL.405196  

   Munoz, Maria_F; Medina, Adam; Autry, Travis_M; Moody, Galan; Siemens, Mark_E; Bristow, Alan_D; Cundiff, Steven_T; Li, Hebin (October 2020, Optics Letters)

   As optical two-dimensional coherent spectroscopy (2DCS) is extended to a broader range of applications, it is critical to improve the detection sensitivity of optical 2DCS. We developed a fast phase-cycling scheme in a non-collinear optical 2DCS implementation by using liquid crystal phase retarders to modulate the phases of two excitation pulses. The background in the signal can be eliminated by combining either two or four interferograms measured with a proper phase configuration. The effectiveness of this method was validated in optical 2DCS measurements of an atomic vapor. This fast phase-cycling scheme will enable optical 2DCS in novel emerging applications that require enhanced detection sensitivity. 

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2. Anti-Parity-Time Symmetric Optical Four-Wave Mixing in Cold Atoms

   https://doi.org/https://doi.org/10.1103/PhysRevLett.123.193604  

   Jiang, Y.; Mei, Y.; Zuo, Y.; Zhai, Y.; Li, J.; Wen, J.; Du, S. (November 2019, Physical review letters)

   Non-Hermitian optical systems with parity-time (PT) symmetry have recently revealed many intriguing prospects that outperform conservative structures. The previous works are mostly rooted in complex arrangements with controlled gain-loss interplay. Here, we demonstrate anti-PT symmetry inherent in the nonlinear optical interaction based upon forward optical four-wave mixing in a laser-cooled atomic ensemble with negligible linear gain and loss. We observe that the pair of frequency modes undergo a nontrivial anti-PT phase transition between coherent power oscillation and optical parametric amplification in presence of a large phase mismatch. 

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3. Designing fast and efficient electrically driven phase change photonics using foundry compatible waveguide-integrated microheaters

   https://doi.org/10.1364/OE.446984  

   Erickson, John_R; Shah, Vivswan; Wan, Qingzhou; Youngblood, Nathan; Xiong, Feng (April 2022, Optics Express)

   Phase change chalcogenides such as Ge₂Sb₂Te₅(GST) have recently enabled advanced optical devices for applications such as in-memory computing, reflective displays, tunable metasurfaces, and reconfigurable photonics. However, designing phase change optical devices with reliable and efficient electrical control is challenging due to the requirements of both high amorphization temperatures and extremely fast quenching rates for reversible switching. Here, we use a Multiphysics simulation framework to model three waveguide-integrated microheaters designed to switch optical phase change materials. We explore the effects of geometry, doping, and electrical pulse parameters to optimize the switching speed and minimize energy consumption in these optical devices. 

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4. Optical dielectric properties of HfO ₂ -based films

   https://doi.org/10.1116/6.0001651  

   Dou, Hongyi; Strkalj, Nives; Zhang, Yizhi; MacManus-Driscoll, Judith L.; Jia, Quanxi; Wang, Haiyan (May 2022, Journal of Vacuum Science & Technology A)

   We report the dielectric Properties of HfO 2 -based films in the optical–high frequency range. The demonstrated tunability of the optical dielectric constant of HfO 2 -based compounds is of great relevance for optoelectronic applications, e.g., high-refractive index dielectrics for nanoantenna and optical coatings for electronic displays. Since the optical dielectric constant of HfO 2 is determined by the electronic structure and its crystal environment, we tune the physical properties of HfO 2 films on MgO by adding different dopants. In this work, we aim to determine the influence of doping together with the resulting crystal structure on the optical dielectric constant. Hence, we studied 20 mol. % Y-doped HfO 2 (HYO), Hf 0.5 Zr 0.5 O 2 (HZO), and Hf 0.5 Ce 0.5 O 2 (HCO). Among the dopants, Y 2 O 3 has the lowest, ZrO 2 an intermediate, and CeO 2 the highest real part of the optical dielectric constant. The optical dielectric constant is found to be lowest in the cubic HYO films. An intermediate dielectric constant is found in HZO films that is predominantly in the monoclinic phase, but additionally hosts the cubic phase. The highest dielectric constant is observed in HCO films that are predominantly in the cubic phase with inclusions of the monoclinic phase. The observed trend is in good agreement with the dominant role of the dopant type in setting the optical dielectric constant. 

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5. Single-Shot Non-Gaussian Measurements for Optical Phase Estimation 125 (12), 120505 (2020).

   https://doi.org/10.1103/PhysRevLett.125.120505  

   DiMario, M T; Becerra, F E (September 2020, Physical review letters)

   null (Ed.)

   Estimation of the properties of a physical system with minimal uncertainty is a central task in quantum metrology. Optical phase estimation is at the center of many metrological tasks where the value of a physical parameter is mapped to the phase of an electromagnetic field and single-shot measurements of this phase are necessary. While there are measurements able to estimate the phase of light in a single shot with small uncertainties, demonstrations of near-optimal single-shot measurements for an unknown phase of a coherent state remain elusive. Here, we propose and demonstrate strategies for single-shot measurements for ab initio phase estimation of coherent states that surpass the sensitivity limit of heterodyne measurement and approach the Cramer-Rao lower bound for coherent states. These single-shot estimation strategies are based on real-time optimization of coherent displacement operations, single photon counting with photon number resolution, and fast feedback. We show that our demonstration of these optimized estimation strategies surpasses the heterodyne limit for a wide range of optical powers without correcting for detection efficiency with a moderate number of adaptive measurement steps. This is, to our knowledge, the most sensitive single-shot measurement of an unknown phase encoded in optical coherent states. 

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