arXiv subjects

Konstantin E. Dorfman

Publications and source records attributed to Konstantin E. Dorfman.

At least 19 recordsLinked to original sources

arXiv2025

Beating the standard quantum limit with single-photon-added coherent states

The standard quantum limit (SQL), also known as the shot-noise limit, defines how quantum fluctuations of light constrain measurement precision. In a benchmark experiment using the Mach-Zehnder interferometer (MZI), where a coherent state with the average photon number $\langle n\rangle$ is combined with an ordinary vacuum input, the SQL for the phase uncertainty is given by the well-known relation $Δφ_{\text{SQL}} = 1/\langle n\rangle$. Using a single photon-added coherent state and a weak coherent state as inputs, we report an enhanced phase sensitivity in MZI surpassing the SQL. In stark contrast to other approaches, we focus on the low-photon-number regime, $\langle n\rangle < 10$, and demonstrate that our scheme offers better phase sensitivity compared to the SQL. Beating the SQL at low photon numbers paves the way for the new generation of devices employed in \textquotedblleft photon-starved\textquotedblright quantum sensing, spectroscopy, and metrology.

quant-ph↗

arXiv2022

Incoherent control of two-photon induced optical measurements in open quantum systems: quantum heat engine perspective

We present a consistent optimization procedure for the optical measurements in open quantum systems using recently developed incoherent control protocol. Assigning an effective hot bath for the two-entangled-photon pump we recast the transmission of classical probe as a work in a quantum heat engine framework. We demonstrate that maximum work in such a heat engine can exceed that for the classical two-photon and one-photon pumps, while efficiency at maximum power can be attributed to conventional boundaries obtained for three-level maser heat engine. Our results pave the way for incoherent control and optimization of optical measurements in open quantum systems that involve two-photon processes with quantum light.

quant-ph↗

arXiv2021

Coherence enhanced quantum-dot heat engine

We show that quantum coherence can enhance the performance of a continuous quantum heat engine in the Lindblad description. We investigate the steady-state solutions of the particle-exchanging quantum heat engine, composed of degenerate double quantum dots coupled to two heat baths in parallel, where quantum coherence may be induced due to interference between relaxation channels. We find that the engine power can be enhanced by the coherence in the nonlinear response regime, when the symmetry of coupling configurations between dots and two baths is broken. In the symmetric case, the coherence cannot be maintained in the steady state, except for the maximum interference degenerate case, where initial-condition-dependent multiple steady states appear with a dark state.

quant-ph↗

arXiv2021

Interferometric-Spectroscopy With Quantum-Light; Revealing Out-of-Time-Ordering Correlators

We survey the inclusion of interferometric elements in nonlinear spectroscopy performed with quantum light. Controlled interference of electromagnetic fields coupled to matter can induce constructive or destructive contributions of microscopic coupling sequences (histories) of matter. Since quantum fields do not commute, quantum light signals are sensitive to the order of light-matter coupling sequence. Matter correlation functions are thus imprinted by different field factors, which depend on that order. We identify the associated quantum information obtained by controlling the weights of different contributing pathways, and offer several experimental schemes for recovering it. Nonlinear quantum response functions include out-of-time-ordering matter correlators (OTOC) which reveal how perturbations spread throughout a quantum system (information scrambling). Their effect becomes most notable when using ultrafast pulse sequences with respect to the path difference induced by the interferometer. OTOC appear in quantum-informatics studies in other fields, including black holes, high energy, and condensed matter physics.

quant-ph↗

arXiv2021

Incoherent control of optical signals; quantum heat engine approach

Optical pump-probe signals can be viewed as work done by the matter while transferring the energy between two coherent baths (from pump to probe). In thermodynamics a heat engine, such as laser, is a device which performs similar work but operating between two thermal baths. We propose an "incoherent" control procedure for the optical signals using the physics of quantum heat engine. By combining a coherent laser excitation of electronic excited state of molecule with thermal relaxation we introduce an effective thermal bath treating stimulated emission of probe photons as work performed by the heat engine. We optimize power and efficiency for the pump-probe signal using control parameters of the pump laser utilizing four level molecular model in strong and weak coupling regime illustrating its equivalence with the thermodynamic cycle of the heat engine.

quant-ph↗

arXiv2021

Hong-Ou-Mandel interferometry and spectroscopy using entangled photons

Optical interferometry has been a long-standing setup for characterization of quantum states of light. Both the linear and the nonlinear interferences can provide information about the light statistics an underlying detail of the light-matter interactions. Here we demonstrate how interferometric detection of nonlinear spectroscopic signals may be used to improve the measurement accuracy of matter susceptibilities. Light-matter interactions change the photon statistics of quantum light, which are encoded in the field correlation functions. Application is made to the Hong-Ou-Mandel two-photon interferometer that reveals entanglement-enhanced resolution that can be achieved with existing optical technology.

quant-ph↗

arXiv2021

Revealing topological phase in Pancharatnam-Berry metasurfaces using mesoscopic electrodynamics

Relying on the local orientation of nanostructures, Pancharatnam-Berry metasurfaces are currently enabling a new generation of polarization-sensitive optical devices. A systematical mesoscopic description of topological metasurfaces is developed, providing a deeper understanding of the physical mechanisms leading to the polarization-dependent breaking of translational symmetry in contrast with propagation phase effects. These theoretical results, along with interferometric experiments, contribute to the development of a solid theoretical framework for arbitrary polarization-dependent metasurfaces.

physics.optics↗

arXiv2019

Quantum phase-sensitive diffraction and imaging using entangled photons

We propose a novel quantum diffraction imaging technique whereby one photon of an entangled pair is diffracted off a sample and detected in coincidence with its twin. The image is obtained by scanning the photon that did not interact with matter. We show that when a dynamical quantum system interacts with an external field, the phase information is imprinted in the state of the field in a detectable way. The contribution to the signal from photons that interact with the sample scales as $\propto I_{p}^{1/2}$, where $I_{p}$ is the source intensity, compared to $\propto I_{p}$ of classical diffraction. This makes imaging with weak-field possible, avoiding damage to delicate samples. A Schmidt decomposition of the state of the field can be used for image enhancement by reweighting the Schmidt modes contributions.

quant-ph↗

arXiv2019

Monitoring Spontaneous Charge-density Fluctuations by Single-molecule Diffraction of Quantum Light

Homodyne X-ray diffraction signals produced by classical light and classical detectors are given by the modulus square of the charge density in momentum space $\left|σ(\mathbf{q})\right|^{2}$, missing its phase which is required in order to invert the signal to real space. We show that quantum detection of the radiation field yields a linear diffraction pattern that reveals $σ(\mathbf{q})$ itself, including the phase. We further show that repeated diffraction measurements with variable delays constitute a novel multidimensional measure of spontaneous charge-density fluctuations. Classical diffraction, in contrast, only reveals a subclass of even-order correlation functions. Simulations of two dimensional signals obtained by two diffraction events are presented for the amino acid cysteine.

physics.chem-ph↗

arXiv2018

Efficiency at Maximum Power of Laser Quantum Heat Engine Enhanced by Noise-Induced Coherence

Quantum coherence has been demonstrated in various systems including organic solar cells and solid state devices. In this letter, we report the lower and upper bounds for the performance of quantum heat engines determined by the efficiency at maximum power. Our prediction based on the canonical 3-level Scovil and Schulz-Dubois maser model strongly depends on the ratio of system-bath couplings for the hot and cold baths and recovers the theoretical bounds established previously for the Carnot engine. Further, introducing a 4-th level to the maser model can enhance the maximal power and its efficiency, thus demonstrating the importance of quantum coherence in the thermodynamics and operation of the heat engines beyond the classical limit.

quant-ph↗

arXiv2016

Time-and-frequency gated photon coincidence counting; a novel multidimensional spectroscopy tool

Coherent multidimensional optical spectroscopy techniques are broadly applied across the electromagnetic spectrum ranging from NMR to the UV. These reveal properties of matter through correlation plots of signal fields generated in response to sequences of short pulses with variable delays. Here we discuss a new class of multidimensional techniques obtained by time-and-frequency resolved photon coincidence counting measurements of N photons which constitutes a 2N dimensional spectrum. A compact description of these signals is developed based on time ordered superoperators rather than the normally ordered ordinary operators used in Glauber's photon counting formalism.The independent control of the time and frequency gate parameters reveals details of matter dynamics not available otherwise. Application to an anharmonic oscillator model with fluctuating energy and anharmonicity demonstrates the power of these signals.

quant-ph↗

arXiv2016

Nonlinear optical signals and spectroscopy with quantum light

Conventional nonlinear spectroscopy uses classical light to detect matter properties through the variation of its response with frequencies or time delays. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. We present an intuitive diagrammatic approach for calculating ultrafast spectroscopy signals induced by quantum light, focusing on applications involving entangled photons with nonclassical bandwidth properties - known as "time-energy entanglement". Nonlinear optical signals induced by quantized light fields are expressed using time ordered multipoint correlation functions of superoperators. These are different from Glauber's g- functions for photon counting which use normally ordered products of ordinary operators. Entangled photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. After a brief survey of properties of entangled photon pairs relevant to their spectroscopic applications, different optical signals, and photon counting setups are discussed and illustrated for simple multi-level model systems.

quant-ph↗

arXiv2015

Catching Conical Intersections in the Act; Monitoring Transient Electronic Coherences by Attosecond Stimulated X-Ray Raman Signals

Conical intersections (CoIn) dominate the pathways and outcomes of virtually all photophysical and photochemical molecular processes. Despite extensive experimental and theoretical effort, CoIns have not been directly observed yet and the experimental evidence is being inferred from fast reaction rates and some vibrational signatures. We show that short X-ray (rather than optical) pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn.

physics.chem-ph↗

arXiv2015

Nonlinear fluctuations and dissipation in matter revealed by quantum light

Quantum optical fields offer numerous control knobs which are not available with classical light and may be used for monitoring the properties of matter by novel types of spectroscopy. It has been recently argued that such quantum spectroscopy signals can be obtained by a simple averaging of their classical spectroscopy counterparts over the Glauber-Sudarshan quasiprobability distribution of the quantum field; the quantum light thus merely provides a novel gating window for the classical response functions. We show that this argument only applies to the linear response and breaks down in the nonlinear regime. The quantum response carries additional valuable information about response and spontaneous fluctuations of matter that may not be retrieved from the classical response by simple data processing. This is connected to the lack of a nonlinear fluctuation-dissipation relation.

quant-ph↗

arXiv2015

Detecting Electronic Coherence by Multidimensional Broadband Stimulated X-Ray Raman Signals

Nonstationary molecular states which contain electronic coherences can be impulsively created and manipulated by using recently-developed ultrashort optical and X-ray pulses via photoexcitation, photoionization and Auger processes. We propose several stimulated-Raman detection schemes that can monitor the phase-sensitive electronic and nuclear dynamics. Three detection protocols of an X-ray broadband probe are compared - frequency dispersed transmission, integrated photon number change, and total pulse energy change. In addition each can be either linear or quadratic in the X-ray probe intensity. These various signals offer different gating windows into the molecular response which is described by correlation functions of electronic polarizabilities. Off-resonant and resonant signals are compared.

physics.chem-ph↗

arXiv2015

Stochastic Liouville Equations for Femtosecond Stimulated Raman Spectroscopy

Electron and vibrational dynamics of molecules are commonly studied by subjecting them to two interactions with a fast actinic pulse that prepares them in a nonstationary state and after a variable delay period $T$, probing them with a Raman process induced by a combination of a broadband and a narrowband pulse. This technique known as femtosecond stimulated Raman spectroscopy (FSRS) can effectively probe time resolved vibrational resonances. We show how FSRS signals can be modeled and interpreted using the stochastic Liouville equations (SLE) originally developed for NMR lineshapes. The SLE provides a convenient simulation protocol that can describe complex dynamics due to coupling to collective coordinates at much lower cost that a full dynamical simulation. The origin of the dispersive features which appear when there is no separation of timescales between vibrational variations and dephasing is clarified.

quant-ph↗

arXiv2015

Evaluation of optical probe signals from nonequilibrium systems

We predict several effects associated with the optical response of systems prepared in a nonequilibrium state by impulsive optical excitations. The linear response depends on the phase of the electric field even if the initial nonequilirbium state has only populations, no coherences. Initial quantum coherences induce additional phase dependence which also shows new resonances in nonlinear wave mixing. In systems strongly driven by an external optical field, the field frequency generates a phase dependent probe absorption. This gives further control to manipulate the relative contribution to the linear signal due to initial populations and coherences.

quant-ph↗

arXiv2014

Noise-induced quantum coherence in photosynthetic complexes with multiple energy transfer pathways

We theoretically investigate exciton relaxation dynamics in molecular aggregates based on model photosynthetic complexes under various conditions of incoherent excitation. We show that noise-induced quantum coherence is generated between spatially-separated exciton states which belong to the same or different energy transfer pathways, coupled via real and virtual transfer processes. Such quantum coherence effects may be used to improve light-harvesting efficiency and to reveal quantum phenomena in biology.

physics.bio-ph↗