arXiv subjects

Hideo Mabuchi

Publications and source records attributed to Hideo Mabuchi.

At least 37 records · Page 2Linked to original sources

arXiv2021

Efficient simulation of ultrafast quantum nonlinear optics with matrix product states

Ultra-short pulses propagating in nonlinear nanophotonic waveguides can simultaneously leverage both temporal and spatial field confinement, promising a route towards single-photon nonlinearities in an all-photonic platform. In this multimode quantum regime, however, faithful numerical simulations of pulse dynamics naïvely require a representation of the state in an exponentially large Hilbert space. Here, we employ a time-domain, matrix product state (MPS) representation to enable efficient simulations by exploiting the entanglement structure of the system. In order to extract physical insight from these simulations, we develop an algorithm to unravel the MPS quantum state into constituent temporal supermodes, enabling, e.g., access to the phase-space portraits of arbitrary pulse waveforms. As a demonstration, we perform exact numerical simulations of a Kerr soliton in the quantum regime. We observe the development of non-classical Wigner-function negativity in the solitonic mode as well as quantum corrections to the semiclassical dynamics of the pulse. A similar analysis of $χ^{(2)}$ simultons reveals a unique entanglement structure between the fundamental and second harmonic. Our approach is also readily compatible with quantum trajectory theory, allowing full quantum treatment of propagation loss and decoherence. We expect this work to establish the MPS technique as part of a unified engineering framework for the emerging field of broadband quantum photonics.

quant-ph↗

arXiv2020

Broadband Parametric Downconversion as a Discrete-Continuum Fano Interaction

We introduce a theoretical framework based on Fano's theory of discrete-continuum interactions to analyze the quantum dynamics of broadband parametric downconversion (PDC) in the few-pump-photon regime of nonlinear quantum nanophotonics. Applying this unified analytic approach to 1D $χ^{(2)}$-nonlinear waveguides, we find a host of remarkable dynamical features due to the coupling of a discrete pump state to the signal continuum, from unit-efficiency (i.e., complete) downconversion when the coupling is dissipative, to Rabi-like oscillations with sub-exponential decay when it is dispersive. The theory provides a straightforward way to analytically compute a full characterization of the PDC dynamics, including the complete eigensystem of the continuum Hamiltonian and expressions for the signal biphoton correlation function. We also apply the theory to study a pair of linearly coupled $χ^{(2)}$ waveguides, where two discrete pump states simultaneously downconvert into a common-mode signal continuum, resulting in Fano interference that critically affects the PDC rate. Under appropriate conditions, the theory predicts characteristic Fano lineshapes and even complete destructive interference resulting in the full suppression of PDC, due to the formation of a bound pump state in the continuum. Generalizing further, we show that the framework can also be applied to higher-order parametric processes such as parametric three-photon generation, and we also find numerical signatures that Fano-type interactions occur even for multi-photon PDC under stronger pumping. Our results establish broadband PDC as yet another physical system natively exhibiting Fano-type interactions and advance a theoretical framework in which to understand the complicated quantum dynamics of strongly nonlinear broadband quantum optics.

quant-ph↗

arXiv2020

Thermo-Optic Multi-Stability and Relaxation in Silicon Microring Resonators with Lateral Diodes

We demonstrate voltage-tunable thermo-optic bi- and tri-stability in silicon photonic microring resonators with lateral p-i-n junctions and present a technique for characterizing the thermo-optic transient response of integrated optical resonators. Our method for thermo-optic transient response measurement is applicable to any integrated photonics platform and uses standard equipment. Thermo-optic relaxation in encapsulated waveguides is found to be approximately logarithmic in time, consistent with the analytic solution for 2D heat diffusion. We develop a model for thermo-optic microring multi-stability and dynamics which agrees with experiment data over a wide range of operating conditions. Our work highlights the fundamental connection in semiconductor waveguides between active free-carrier removal and thermo-optic heating, a result of particular relevance to Kerr soliton state stability and on-chip frequency comb generation. The devices studied here were fabricated in a CMOS foundry process and as a result our model is useful for design of silicon photonic waveguide devices.

physics.optics↗

arXiv2019

Engineering a Kerr-based Deterministic Cubic Phase Gate via Gaussian Operations

We propose a deterministic, measurement-free implementation of a cubic phase gate for continuous-variable quantum information processing. In our scheme, the applications of displacement and squeezing operations allow us to engineer the effective evolution of the quantum state propagating through an optical Kerr nonlinearity. Under appropriate conditions, we show that the input state evolves according to a cubic phase Hamiltonian, and we find that the cubic phase gate error decreases inverse-quartically with the amount of quadrature squeezing, even in the presence of linear loss. We also show how our scheme can be adapted to deterministically generate a nonclassical approximate cubic phase state with high fidelity using a ratio of native nonlinearity to linear loss of only $10^{-4}$, indicating that our approach may be experimentally viable in the near term even on all-optical platforms, e.g., using quantum solitons in pulsed nonlinear nanophotonics.

quant-ph↗

arXiv2019

Low-Temperature Annihilation Rate for Quasi-Localized Excitons in Monolayer MoS2

The strong Coulomb forces in monolayer transition metal dichalcogenides ensure that optical excitation of band electrons gives rise to Wannier-Mott excitonic states, each of which can be conceptualized as a composite of a Gaussian wavepacket corresponding to center-of-mass motion and an orbital state corresponding to the motion of the electron and hole about the center-of-mass. Here, we show that at low temperature in monolayer MoS2, given quasi-localized excitons and consequently a significant inter-exciton spacing, the excitons undergo dipole-dipole interaction and annihilate one another in a manner analogous to Auger recombination. To construct our model, we assume that each exciton is localized in a region whose length is on the same scale as the excitonic diameter, thus causing the exciton to behave in a fermionic manner, while the distance between neighboring excitons is much larger than the exciton diameter. We construct the orbital ladder operators for each exciton and apply Fermi's Golden Rule to derive the overall recombination rate as a function of exciton density.

cond-mat.mes-hall↗

arXiv2019

Nonlinear optical response of a local surface plasmon coupled to a 2D material

We present a theoretical study of the optical response of a nonlinear oscillator formed by coupling a metal nanoparticle local surface plasmon resonance to excitonic degrees of freedom in a monolayer transition-metal dichalcogenide. We show that the combined system should exhibit strong anharmonicity in its low-lying states, predicting for example a seven order-of-magnitude increase in nonlinearity relative to a silicon photonic crystal cavity. Then, we demonstrate that such system exhibits strong quantum features such as antibunching and non-Gaussianity. Arrays of such nanoscale nonlinear oscillators could be used to realize novel optical metamaterials; alternatively, an individual nanoparticle-monolayer construct could be coupled to an optical resonator to mediate efficient input-output coupling to propagating fields.

cond-mat.mes-hall↗

arXiv2019

Embedding entanglement generation within a measurement-feedback coherent Ising machine

We present a new scheme to efficiently establish entanglement between optical modes in a time-multiplexed coherent Ising machine (CIM) by means of nonlocal measurement and feedback. We numerically simulate and evaluate the generation of steady-state entanglement in a system with nearest-neighbor interactions on a 1D ring, and we compare the results to those of a conventional CIM with all-optical interactions mediated by delay lines. We show that the delay-line architecture has a fundamental limit on accessible entanglement that our measurement-based scheme can substantially surpass. These results motivate the study of non-classical correlations in CIMs with levels of entanglement previously considered to be experimentally impractical.

quant-ph↗

arXiv2019

Experimental investigation of performance differences between Coherent Ising Machines and a quantum annealer

Physical annealing systems provide heuristic approaches to solving NP-hard Ising optimization problems. Here, we study the performance of two types of annealing machines--a commercially available quantum annealer built by D-Wave Systems, and measurement-feedback coherent Ising machines (CIMs) based on optical parametric oscillator networks--on two classes of problems, the Sherrington-Kirkpatrick (SK) model and MAX-CUT. The D-Wave quantum annealer outperforms the CIMs on MAX-CUT on regular graphs of degree 3. On denser problems, however, we observe an exponential penalty for the quantum annealer ($\exp(-α_\textrm{DW} N^2)$) relative to CIMs ($\exp(-α_\textrm{CIM} N)$) for fixed anneal times, on both the SK model and on 50%-edge-density MAX-CUT, where the coefficients $α_\textrm{CIM}$ and $α_\textrm{DW}$ are problem-class-dependent. On instances with over $50$ vertices, a several-orders-of-magnitude time-to-solution difference exists between CIMs and the D-Wave annealer. An optimal-annealing-time analysis is also consistent with a significant projected performance difference. The difference in performance between the sparsely connected D-Wave machine and the measurement-feedback facilitated all-to-all connectivity of the CIMs provides strong experimental support for efforts to increase the connectivity of quantum annealers.

quant-ph↗

arXiv2019

Coherent Control of Two-Dimensional Excitons

Electric dipole radiation can be controlled by coherent optical feedback, as has previously been studied by modulating the photonic environment for point dipoles placed both in optical cavities and near metal mirrors. In experiments involving fluorescent molecules, trapped ions and quantum dots the point nature of the dipole, its sub-unity quantum efficiency, and decoherence rate conspire to severely limit any change in total linewidth. Here we show that the transverse coherence of exciton emission in the monolayer two-dimensional (2D) material MoSe${}_2$ removes many of the fundamental physical limitations present in previous experiments. The coherent interaction between excitons and a photonic mode localized between the MoSe${}_2$ and a nearby planar mirror depends interferometrically on mirror position, enabling full control over the radiative coupling rate from near-zero to 1.8 meV and a corresponding change in exciton total linewidth from 0.9 to 2.3 meV. The highly radiatively broadened exciton resonance (a ratio of up to $3:1$ in our samples) necessary to observe this modulation is made possible by recent advances in 2D materials sample fabrication. Our method of mirror translation is free of any coupling to strain or DC electric field in the monolayer, which allows a fundamental study of this photonic effect. The weak coherent driving field in our experiments yields a mean excitation occupation number of ${\sim} 10^{-3}$ such that our experiments correspond to probing radiative reaction in the regime of perturbative quantum electrodynamics. This system will serve as a testbed for exploring new excitonic physics and quantum nonlinear optical effects.

cond-mat.mes-hall↗

arXiv2018

Adiabatic Fock state generation scheme using Kerr nonlinearity

We propose a theoretical scheme to deterministically generate Fock states in a Kerr cavity thorough adiabatic variation of the driving field strength and the cavity detuning. We show that the required time to generate a $n$-photon Fock state scales as the square root of $n$. Requirements for the Kerr coefficient relative to the system decoherence rate are provided as a function of desired state fidelity, indicating that the scheme is potentially realizable with the present state of the art in microwave superconducting circuits.

quant-ph↗

arXiv2018

Laser Annealing for Radiatively Broadened MoSe2 grown by Chemical Vapor Deposition

We report on a laser annealing procedure which greatly improves the quality of suspended monolayers of chemical vapor deposition (CVD) grown MoSe2. Annealing with a green laser locally heats the suspended flake to approximately 600 K, which both removes contaminants and reduces strain gradients. At 4 K, we observe linewidths as narrow as 3.5 meV (1.6nm) full-width at half-max (FWHM) for both photoluminescence (PL) and reflection. Large peak reflectances up to 47% are also observed. These values are comparable to those of the highest quality hexagonal boron nitride (hBN) encapsulated samples. We demonstrate that this laser annealing process can yield highly spatially homogeneous samples, with the length scale of the homogeneity limited primarily by the size of the suspended area. Annealed regions are very stable, exhibiting negligible deterioration over 24 hours at cryogenic temperatures. The annealing method is also very repeatable, with substantial improvements of sample quality on every spot (> 40) tested.

cond-mat.mtrl-sci↗

arXiv2018

Factorization of Linear Quantum Systems with Delayed Feedback

We consider the transfer functions describing the input-output relation for a class of linear open quantum systems involving feedback with nonzero time delays. We show how such transfer functions can be factorized into a product of terms which are transfer functions of canonical physically realizable components. We prove under certain conditions that this product converges, and can be approximated on compact sets. Thus our factorization can be interpreted as a (possibly infinite) cascade. Our result extends past work where linear open quantum systems with a state-space realization have been shown to have a pure cascade realization [Nurdin, H. I., Grivopoulos, S., & Petersen, I. R. (2016). The transfer function of generic linear quantum stochastic systems has a pure cascade realization. Automatica, 69, 324-333.]. The functions we consider are inherently non-Markovian, which is why in our case the resulting product may have infinitely many terms.

quant-ph↗

arXiv2018

Optical nonlinearities of excitons in monolayer MoS2

We calculate linear and nonlinear optical susceptibilities arising from the excitonic states of mono- layer MoS2 for in-plane light polarizations, using second-quantized bound and unbound exciton operators. Optical selection rules are critical for obtaining the susceptibilities. We derive the valley-chirality rule for the second harmonic generation in monolayer MoS2, and find that the third- harmonic process is efficient only for linearly polarized input light while the third-order two photon process (optical Kerr effect) is efficient for circularly polarized light using a higher order exciton state. The absence of linear absorption due to the band gap and the unusually strong two-photon third-order nonlinearity make the monolayer MoS2 excitonic structure a promising resource for coherent nonlinear photonics.

cond-mat.mes-hall↗

arXiv2017

Low dimensional manifolds for exact representation of open quantum systems

Weakly nonlinear degrees of freedom in dissipative quantum systems tend to localize near manifolds of quasi-classical states. We present a family of analytical and computational methods for deriving optimal unitary model transformations based on representations of finite dimensional Lie groups. The transformations are optimal in that they minimize the quantum relative entropy distance between a given state and the quasi-classical manifold. This naturally splits the description of quantum states into quasi-classical coordinates that specify the nearest quasi-classical state and a transformed quantum state that can be represented in fewer basis levels. We derive coupled equations of motion for the coordinates and the transformed state and demonstrate how this can be exploited for efficient numerical simulation. Our optimization objective naturally quantifies the non-classicality of states occurring in some given open system dynamics. This allows us to compare the intrinsic complexity of different open quantum systems.

quant-ph↗

arXiv2016

Reduced models and design principles for half-harmonic generation in synchronously-pumped optical parametric oscillators

We develop reduced models that describe half-harmonic generation in a synchronously-pumped optical parametric oscillator above threshold, where nonlinearity, dispersion, and group-velocity mismatch are all relevant. These models are based on (1) an eigenmode expansion for low pump powers, (2) a simulton-like sech-pulse ansatz for intermediate powers, and (3) dispersionless box-shaped pulses for high powers. Analytic formulas for pulse compression, degenerate vs. nondegenerate operation, and stability are derived and compared to numerical and experimental results.

physics.optics↗

arXiv2016

Comprehensive analysis of the optical Kerr coefficient of graphene

We present a comprehensive analysis of the the nonlinear optical Kerr effect in graphene. We directly solve the S-matrix element to calculate the absorption rate, utilizing the Volkov-Keldysh- type crystal wave functions. We then convert to the nonlinear refractive index coefficients through the Kramers-Kronig relation. In this formalism, the source of Kerr nonlinearity is the interplay of optical fields that cooperatively drive the transition from valence to conduction band. This formalism makes it possible to identify and compute the rates of distinct nonlinear processes that contribute to the Kerr nonlinear refractive index coefficient. The four identified mechanisms are two photon absorption, Raman transition, self coupling, and quadratic AC Stark effect. We also present a comparison of our theory with recent experimental and theoretical results.

cond-mat.mes-hall↗

arXiv2016

Topological defect formation in 1D and 2D spin chains realized by network of optical parametric oscillators

A network of optical parametric oscillators is used to simulate classical Ising and XY spin chains. The collective nonlinear dynamics of this network, driven by quantum noise rather than thermal fluctuations, seeks out the Ising / XY ground state as the system transitions from below to above the lasing threshold. We study the behavior of this "Ising machine" for three canonical problems: a 1D ferromagnetic spin chain, a 2D square lattice, and problems where next-nearest-neighbor couplings give rise to frustration. If the pump turn-on time is finite, topological defects form (domain walls for the Ising model, winding number and vortices for XY) and their density can be predicted from a numerical model involving a linear "growth stage" and a nonlinear "saturation stage". These predictions are compared against recent data for a 10,000-spin 1D Ising machine.

physics.optics↗

arXiv2016

Trapped Modes in Linear Quantum Stochastic Networks with Delays

Networks of open quantum systems with feedback have become an active area of research for applications such as quantum control, quantum communication and coherent information processing. A canonical formalism for the interconnection of open quantum systems using quantum stochastic differential equations (QSDEs) has been developed by Gough, James and co-workers and has been used to develop practical modeling approaches for complex quantum optical, microwave and optomechanical circuits/networks. In this paper we fill a significant gap in existing methodology by showing how trapped modes resulting from feedback via coupled channels with finite propagation delays can be identified systematically in a given passive linear network. Our method is based on the Blaschke-Potapov multiplicative factorization theorem for inner matrix-valued functions, which has been applied in the past to analog electronic networks. Our results provide a basis for extending the Quantum Hardware Description Language (QHDL) framework for automated quantum network model construction (Tezak \textit{et al.} in Philos. Trans. R. Soc. A, Math. Phys. Eng. Sci. 370(1979):5270-5290, to efficiently treat scenarios in which each interconnection of components has an associated signal propagation time delay.

quant-ph↗