Tai Hyun Yoon

Current optical atomic clocks do not utilize their resources optimally. In particular, an exponential gain in sensitivity could be achieved if multiple atomic ensembles were to be controlled or read out individually, even without entanglement. However, controlling optical transitions locally remains an outstanding challenge for neutral-atom-based clocks and quantum computing platforms. Here we show arbitrary, single-site addressing for an optical transition via sub-wavelength controlled moves of atoms trapped in tweezers. The scheme is highly robust as it relies only on the relative position changes of tweezers and requires no additional addressing beams. Using this technique, we implement single-shot, dual-quadrature readout of Ramsey interferometry using two atomic ensembles simultaneously, and show an enhancement of the usable interrogation time at a given phase-slip error probability. Finally, we program a …

We present a versatile method for producing two-mode stabilized squeezed coherent state (SSCS) of light with controllable nonclassicality. Our method involves seeding phasecoherent bichromatic fields into a nondegenerate optical parametric oscillator (OPO), where the global phase difference Φ between the bichromatic seed and pump fields plays a central role. When Φ= 2????????, where ???? is an integer, the squeezing rate is high, and the amplitudes of bichromatic seed fields are weak, we show that the two-mode SSCS has its nonclassical measure at its minimum possible value with an effective displacement that compensates for single-photon losses with injected photons. As a result, the SSCS has a larger mean photon number and controllable nonclassicality compared to an OPO without seed fields. We also show that near-perfect squeezing level can be obtained at that effective displacement without being subject to injection rates. We believe that the proposed quantum source of two-mode SSCS with controllable nonclassicality would be useful for continuous-variable photonic quantum information processing.

We consider a two-mode stabilized squeezed coherent state (SSCS) of light and introduce the indicator, a novel measure for characterizing nonclassicality in the resulting EPR-entangled state. Unlike existing methods based on Cauchy-Schwarz or Murihead inequalities, leverages analytical solutions to the quantum Langevin equations to directly analyze nonclassicality arising from key processes like bichromatic injection, frequency conversion, and parametric down-conversion (both spontaneous and stimulated). This approach not only identifies the optimal phase for maximum nonclassicality but also reveals two new phenomena: first, both intra-cavity and extra-cavity fields exhibit the same degree of nonclassicality, and second, balanced seeding in phase-mismatched configurations induces nonclassicality across a broad range of squeezing and seeding parameters. Our work deepens the understanding of the intricate dependence of nonclassicality on system parameters in the context of SSCS, paving the way for investigations into the quantum-to-classical transition in entangled systems. The potential of holds significant promise for advancements in quantum optics and information science.

Tellurium (Te) microcrystal with a bandgap of approximately 0.37 eV is a potentially useful semiconducting material exhibiting ultrafast electronic relaxation processes. To measure the intervalley and intravalley relaxation rates, we carried out two-color near-IR (NIR) pump and mid-IR (MIR) probe studies of rod-type Te microcrystals, employing a repetition-frequency-stabilized NIR (800 nm) laser and an MIR (3300 nm) frequency comb. Using interferometrically detected two-color asynchronous sampling (AS) transient absorption (TA) spectroscopy, we measured time- and frequency-resolved TA signals of rod-type Te microcrystals. The frequency-resolved and excitation-intensity-dependent AS-TA signals show that the charge carriers undergo relaxation processes with different time constants after photoexcitation. In this work, we found that there are three distinguishable relaxation components that correspond to an …

An apparatus for individually trapping atoms, individually imaging the atoms, and individually cooling the atoms to prevent loss of the atoms from the trap caused by the imaging. The apparatus can be implemented in various quantum computing, sensing, and metrology applications (eg, in an atomic clock).

Time-resolved multidimensional spectroscopy is an advanced spectroscopic technique that can be used to study the molecular structure and dynamics of chromophores in condensed phases by probing multiple resonances of chemical and biophysical systems. To achieve such a multidimensional measurement, the nonlinear optical response of materials should be measured for varying time delays between multiple optical pulses. Inevitably, the data acquisition time dramatically increases with the number of dimensions and the length of each time-delay scan. Therefore, technical breakthroughs toward improved data acquisition rates and time resolutions have long been sought for more versatile and extensive use of coherent multidimensional spectroscopy. Here, we present a tutorial description of the concepts and methods of coherent multidimensional spectroscopy with multiple repetition-frequency-stabilized …

We carried out transient absorption spectroscopy of thioflavin T (ThT) molecules in various solvents employing an asynchronous optical sampling (ASOPS) scheme with dual synchronized and frequency up-converted mode-lock lasers in the near UV (NUV) spectral region. We developed a pair of synchronized femtosecond lasers with tunable center wavelengths ranging from 380 to 430 nm and spectral bandwidths of 30 nm. As a proof-of-principle experiment, we measured interferometrically detected time and frequency-resolved pump–probe signals of ThT in various solvents to study the twisted intramolecular charge transfer process of photo-excited ThT molecules. Both single-color NUV-NUV and two-color NUV-near IR (NIR) pump–probe measurements reveal that the vibronic coupling strengths of two vibrational modes with frequencies of 214 and 526 cm− 1 in the excited state of ThT are reduced when ThT is …

Exciton relaxation dynamics in multichromophore systems are often modeled using Redfield theory, where bath fluctuations mediate the relaxation among the exciton eigenstates. Identifying the vibrational or phonon modes that are implicated in exciton relaxation allows more detailed understanding of exciton dynamics. Here we focus on a well-studied light-harvesting II complex (LH2) isolated from the photosynthetic purple bacterium Rhodoblastus acidophilus strain 10050. Using two synchronized mode-locked lasers, we carried out a polarization-dependent two-dimensional electronic spectroscopy (2DES) study of an ultrafast exciton relaxation in the B850 band of LH2. 2DES data with different polarization configurations enable us to investigate the exciton relaxation between the k = ±1 exciton states. Then, we identify vibrational modes coupled to the exciton relaxation by analyzing the coherent wavepackets in …

We demonstrate continuous loading of strontium atoms into a high finesse ring cavity and observe continuous strong collective coupling in the form of a vacuum Rabi splitting between the atoms and the cavity on the 7.5 kHz transition to . The atoms are loaded into the cavity from a 3D narrow linewidth molasses, thus avoiding large magnetic field gradients and associated broadening of transition frequencies. The ring cavity allows us to realize a deterministic conveyor belt to transport atoms away from the loading region where the laser cooling beams lead to broadening of the strontium clock transition. We trap up to atoms in an intracavity 813 nm lattice in the Lamb-Dicke regime, and transport the atoms along the cavity axis. This work opens the path to the creation of a continuous wave superradiant laser with millihertz linewidth enabling searches for new physics and the use of high-precision optical frequency references outside of low vibration laboratory environments.

A theoretical model of an underdamped harmonic oscillator (UHO) driven by periodic short pulses may find plenty of applications in classical, semiclassical, and quantum physics. We present here two different forms of analytical solutions: {\it time-periodic solutions} and {\it harmonic solutions} for one-dimensional classical UHO driven by three different trains of short pulses. They are a Dirac comb, a train of square pulses, and a train of Gaussian pulses with the same pulse-to-pulse time interval and pulse width . Two solutions for square and Gaussian pulses approach to that of the Dirac comb when the pulse width as expected. In particular, the harmonic solutions for Dirac comb and Gaussian pulses could be expressed approximately with harmonic terms of the repetition frequency up to the second order. The presented analytical solutions would provide a practical way to determine experimentally the system parameters such as the underdamped oscillation frequency , the natural frequency , and the damping rate , by nonlinear curve fitting procedures for different driving force parameters of and .

To test the principle of complementarity and wave-particle duality quantitatively, we need a quantum composite system that can be controlled by experimental parameters. Here, we demonstrate that a double-path interferometer consisting of two parametric downconversion crystals seeded by coherent idler fields, where the generated coherent signal photons are used for quantum interference and the conjugate idler fields are used for which-path detectors with controllable fidelity, is useful for elucidating the quantitative complementarity. We show that the quanton source purity μs is tightly bounded by the entanglement E between the quantons and the remaining degrees of freedom by the relation μs=1−E2, which is experimentally confirmed. We further prove that the experimental scheme using two stimulated parametric downconversion processes is an ideal tool for investigating and understanding wave-particle …

Interferometric spectroscopy with undetected photons (ISUP) utilizing quantum mechanically path-entangled photon pairs has received considerable attention as an optical-measurement platform. Recently, we carried out a proof-of-concept experiment to show that ISUP can be used to measure the transmission spectrum of a Fabry-Perot resonator. Here, we demonstrate that ISUP with dual stimulated parametric down-conversion (StPDC) processes, which allows us to perform infrared rovibrational spectroscopy with visible photons. In our ISUP method, quantum coherence between two independent signal photons from each StPDC crystal is induced by the indistinguishability of conjugate idler fields and results in high visibility of the signal single-photon interferometry at the nondegenerate wavelength. If the seed-beam intensity is imbalanced due to the sample absorption, the corresponding envelope modulation of …

Mid-infrared (mid-IR) spectroscopy is an incisive tool for studying structures and dynamics of complicated molecules in condensed phases. Developing a compact and broadband mid-IR spectrometer has thus been a long-standing challenge. Here, we show that a highly coherent and broadband mid-IR frequency comb can be generated by using an intrapulse difference-frequency-generation with a train of pulses from a few-cycle pulse Ti:sapphire oscillator. By tightly focusing the oscillator output beam into a single-pass, fan-out-type periodically poled lithium niobate crystal and tilting the orientation of the crystal, we show that a mid-IR frequency comb with more than an octave spectral bandwidth from 1550 cm–1 (46 THz) to 3650 cm–1 (110 THz) and vanishing carrier-envelope-offset phase can be generated. Using two coherent mid-IR frequency combs with different repetition frequencies, we demonstrate that a …

We apply independent component analysis (ICA) to real data from a gravitational wave detector for the first time. Specifically, we use the iKAGRA data taken in April 2016, and calculate the correlations between the gravitational wave strain channel and 35 physical environmental channels. Using a couple of seismic channels which are found to be strongly correlated with the strain, we perform ICA. Injecting a sinusoidal continuous signal in the strain channel, we find that ICA recovers correct parameters with enhanced signal-to-noise ratio, which demonstrates the usefulness of this method. Among the two implementations of ICA used here, we find the correlation method yields the optimal results for the case of environmental noise acting on the strain channel linearly.

We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star–black hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible …

A complete understanding of a photochemical reaction dynamics begins with real-time measurements of both electronic and vibrational structures of photoexcited molecules. Time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS) with femtosecond actinic pump, Raman pump, and Raman probe pulses is one of the incisive techniques enabling one to investigate the structural changes of photoexcited molecules. Herein, we demonstrate that such femtosecond TR-ISRS is feasible with synchronized triple mode-locked lasers without using any time-delay devices. Taking advantage of precise control of the three repetition rates independently, we could achieve automatic scanning of two delay times between the three pulses, which makes both rapid data acquisition and wide dynamic range measurement of the fifth-order TR-ISRS signal achievable. We thus anticipate that the present triple mode-locked …

Following the observation of long-lived coherences in the two-dimensional (2D) electronic spectra of the Fenna-Matthews-Olson (FMO) complex, many theoretical works suggest that coherences between excitons may play a role in the efficient energy transfer that occurs in photosynthetic antennae. This interpretation of the dynamics depends on the assignment of quantum beating signals to superpositions of excitons, which is complicated by the possibility of observing both electronic and vibrational coherences in 2D spectra. Here, we explore 2D spectra of bacteriochlorophyll a (BChla) in solution in an attempt to isolate vibrational beating signals in the absence of excitonic signals to identify the origin of the quantum beats in 2D spectra of FMO. Even at high laser power, our BChla spectra show strong beating only from the nonresonant response of the solvent. The beating signals that we can conclusively assign to …

Mid-infrared (mid-IR) spectroscopy provides a way to study structures and dynamics of complicated molecules in condensed phases. Therefore, developing compact and broadband mid-IR spectrometer has been a long-standing challenge. Here, we show that a highly coherent and broadband mid-IR frequency comb can be generated by using an intra-pulse difference-frequency-generation with a train of pulses from a few-cycle Ti:Sapphire oscillator. By tightly focusing the oscillator output beam into a single-pass fan-out-type periodically-poled lithium niobate crystal and tilting the orientation of the crystal with respect to incident beam, it is shown that mid-IR frequency comb with more than an octave spectral bandwidth from 1550 cm-1 (46 THz) to 3650 cm-1 (110 THz) and vanishing carrier-envelop offset phase can be generated. Then, using two coherent mid-IR frequency combs, we demonstrate that ultrabroad mid-IR dual frequency comb spectroscopy of both aromatic compounds and amino acids in solutions is experimentally feasible. We thus anticipate that our mid-IR frequency combs could be used to further develop ultrafast and broadband IR spectroscopy of chemically reactive and biological molecules in condensed phases.

We present a phase-stable and selectable repetition-rate (f rep) divider (PSRD) of an optical frequency comb (OFC) by down-picking a train of pulses from the fundamental OFC phase coherently. The PSRD operating at the integer pulse-picking order p uses an acousto-optic modulator driven by a train of phase-synchronized single-cycle wave packets oscillating at the carrier frequency of f c≡ f rep and the gating frequency of f g p≡ f rep/p. The demonstrated PSRD can selectively pick a train of pulses with p= 2 to 25 from the fundamental OFC with f rep= 250 MHz at 530 nm. Integrated phase noises from 10 Hz to 25 kHz offset frequency from the optical beat note between each down-picked OFC and the fundamental OFC are measured to be about (59±6) mrad through the whole pulse picking order. The phase-coherent down-picked OFC could be of use for various applications where phase-stable and repetition …

KAGRA is a 3-km interferometric gravitational wave telescope located in the Kamioka mine in Japan. It is the first km-class gravitational wave telescope constructed underground to reduce seismic noise, and the first km-class telescope to use cryogenic cooling of test masses to reduce thermal noise. The construction of the infrastructure to house the interferometer in the tunnel, and the initial phase operation of the interferometer with a simple 3-km Michelson configuration have been completed. The first cryogenic operation is expected in 2018, and the observing runs with a full interferometer are expected in 2020s. The basic interferometer configuration and the current status of KAGRA are described.