UPCOMING TALK:
Date and time: -2025 at 4:00pm Moscow time.
Link to join the seminar: 5fnm6kei.ktalk.ru/dinpfgj9sxrn
Title of the talk:
Speaker:
Abstract:
DELIVERED TALKS
Number: 1
03-Dec-2024 at 4pm Moscow time.
Title of the talk: Polarization squeezing in chalcogenide fibers
Speaker: Prof. Alexey V. Andrianov
Abstract:
We experimentally demonstrate the generation of polarization-squeezed light in a short piece of solid-core chalcogenide (ChG) (As2S3) fiber via the Kerr effect for femtosecond pulses at 1.56 µm. Directly measured squeezing of −2.8 dB is obtained in a setup without active stabilization. Numerical simulations are in good agreement with the experimental results and indicate that the measured squeezing in our setup is mainly limited by the losses in the detection system rather than by the fiber properties.
The talk is based on the paper "Polarization squeezing in chalcogenide fibers" published in Optics Letters 2024.
Link to the publication: https://opg.optica.org/ol/abstract.cfm?URI=ol-49-23-6661
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=44911&option_lang=rus
Number: 2
18-Dec-2024 at 4pm Moscow time.
Title of the talk: Algebraic approach to dynamics of open multimode bosonic systems
Speaker: Dr. Andrei A. Gaidash
Authors: Andrei Gaidash, Alexei D. Kiselev, George Miroshnichenko, Anton Kozubov
Abstract: Quantum dynamics of open continuous variable systems is a multifaceted, rapidly evolving field of both fundamental and technological significance. An important example is a multimode photonic system coupled to a Markovian bath (the environmental correlation times are shorter than the system's relaxation or decoherence time) so that the density matrix dynamics is governed by the master equation of the Lindblad form. Using currently available methods, theoretical analysis of the Lindblad dynamics complicated by intermode couplings can be rather involved even for exactly soluble models. The algebraic approach suggested in this paper simplifies both quantitative and qualitative analysis of the intermode-coupling-induced effects in multimode systems by reducing the Lindblad equation to the form determined by the effective Hamiltonian. Specifically, we develop the algebraic method based on the Lie algebra of quadratic combinations of left and right superoperators associated with matrices to study the Lindblad dynamics of multimode bosonic systems coupled with a thermal bath and described by the Liouvillian superoperator that takes into account both dynamical (coherent) and environment mediated (incoherent) interactions between the modes. Our algebraic technique is applied to transform the Liouvillian into the diagonalized form by eliminating jump superoperators and solve the spectral problem. The temperature independent effective non-Hermitian Hamiltonian, $\hat{H}_{\ind{eff}}$, is found to govern both the diagonalized Liouvillian and the spectral properties. It is shown that the Liouvillian exceptional points are represented by the points in the parameter space where the matrix, $H$, associated with $\hat{H}_{\ind{eff}}$ is non-diagonalizable. We use our method to derive the low-temperature approximation for the superpropagator and to study the special case of a two mode system representing the photonic polarization modes,e.g. optical polarization qubit.For this system, we describe the geometry of exceptional points in the space of frequency and relaxation vectors parameterizing the intermode couplings and, for a single-photon state, evaluate the time dependence of the density matrix.
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=44912&option_lang=rus
Number: 3
9-Jan-2025 at 4pm Moscow time.
Title of the talk: Trapping wave fields in an expulsive potential by means of linear coupling
Speaker: Prof. Boris A. Malomed
Authors: Nir Hacker and Boris Malomed
Abstract: We demonstrate the existence of confined states in one- and two-dimensional (1D and 2D) systems of two linearly-coupled components, with the confining harmonic-oscillator (HO) potential acting upon one-component, and an expulsive anti -HO potential acting upon the other. The systems can be implemented in optical and BEC dual-core waveguides. In the 1D linear system, codimension-one solutions are found in an exact form for the ground state (GS) and dipole mode (the first excited state). Generic solutions are produced by the variational approximation, and are found in a numerical form. Exact codimension-one solutions and generic numerical ones are obtained for the GS and vortex states in the 2D system. Both the trapped and anti-trapped components of the bound states may be dominant ones, in terms of the norm. The localized modes may be categorized as bound states in continuum, as they coexist with delocalized ones. The1D states, as well as the GS in 2D, are weakly affected and remain stable if the self-attractive or repulsive nonlinearity is added to the system. The self-attraction makes the vortex states unstable against splitting, while they remain stable under the action of the self-repulsion.
Publications:
N. Hacker and B. A. Malomed, Nonlinear dynamics of wave packets in tunnel-coupled harmonic-oscillator traps, Symmetry 13, 372 (2021);
Trapping wave fields in an expulsive potential by means of linear coupling, Phys. Rev. E 105, 034213(2022).
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=44963&option_lang=rus
Number: 4
21-Jan-2025 at 4pm Moscow time.
Title of the talk: Recognition of Light Orbital-Angular-Momentum Superpositions for Quantum Communication
Speaker: Prof. Antonio Zelaquett Khoury
Abstract: We study the tomography of spatial qudits encoded on structured light photons in the space of fixed order transverse modes. While direct position measurements with cameras do not provide an informationally complete Positive Operator Valued Measure (POVM), this property is achieved with the use of astigmatic transformation, allowing full characterization of the spatial quantum state from simple intensity measurements in both the intense and in the low photocount regimes. These methods are useful for classical and quantum communication with structured light and will be tested in a quantum network being set up in the Rio de Janeiro metropolitan area.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=44977&option_lang=rus
Number: 5
06-Feb-2025 at 4pm Moscow time.
Title of the talk: Lindblad dynamics of multi-mode photonic systems: Exceptional points and speed of evolution
Speaker: Prof. Alexei D. Kiselev
Abstract: This talk deals with intermode-interaction-induced effects in dynamics of open multi-mode photonic systems representing a family of continuous variable systems whose density matrix dynamics is governed by the master equation of the Lindblad form (the so-called Gorini-Kossakowski-Sudarshan-Lindblad master equation). We briefly discuss two analytical techniques to perform theoretical analysis of the Lindblad dynamics complicated by intermode couplings: (a) an algebraic approach based on the algebra of bilinear superoperators recently suggested in [Gaidash et al., arXiv:2412.13890[quant-phys]] and (b) the method of characteristic functions. We employ exact solution of the thermal bath Lindblad master equation with the Liouvillian superoperator that takes into account both dynamic (coherent) and environment induced (incoherent) intermode couplings to study the speed of evolution and the quantum speed limit (QSL) times of an open multi-mode bosonic system. For Gaussian states, we derive explicit expressions for the evolution speed and the QSL times. General analytical results are applied to the special case of a two-mode system where the intermode couplings can be parametrized using the two intermode coupling vectors: the frequency vector and the relaxation rate vector. For this system, we describe the geometry of Liouvillian exceptional points in the space of these vectors and present a number of numerical results on evolution of Gaussian (two-mode squeezed states) and non-Gaussian (polarization qubit states) states.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45016&option_lang=rus
Number: 6
13-Feb-2025 at 4pm Moscow time.
Title of the talk: Non-Markovian Quantum Stochastic Models
Speaker: Prof. John Gough
Abstract: We give a derivation of the non-Markovian quantum state diffusion equation of Diósi and Strunz starting from a model of a quantum mechanical system coupled to a bosonic bath. We show that the complex trajectories arises as a consequence of using the Bargmann-Segal (complex wave) representation of the bath. In particular, we construct a reproducing kernel Hilbert space for the bath auto-correlation and realize the space of complex trajectories as a Hilbert subspace. The reproducing kernel naturally arises from a feature space where the underlying feature space is the one-particle Hilbert space of the bath quanta. We exploit this to derive the unravelling of the open quantum system dynamics and show equivalence to the equation of Diósi and Strunz.
We also give an explicit expression for the reduced dynamics of a two-level system coupled to the bath via a Jaynes-Cummings interaction and show that this does indeed correspond to an exact solution of the Diósi-Strunz equation. Finally, we discuss the physical interpretation of the complex trajectories and show that they are intrinsically unobservable.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45068&option_lang=rus
Number: 7
16-Feb-2025 at 4pm Moscow time.
Title of the talk: Entanglement dynamics of many body quantum states with evolving system conditions
Speaker: Prof. Pragya Shukla*
Abstract: The entanglement analysis of a pure state of a many body quantum system requires a prior information about its density matrix/ state matrix, obtained in principle by solving the Hamiltonian matrix. The missing information due to complexity of the many body interactions however renders it necessary to consider an ensemble of Hamiltonians and thereby an ensemble for each eigenstate. This in turn leaves a statistical description of the entanglement measures as the only option. For an ensemble to appropriately represent a many body Hamiltonian, the ensemble parameters must be determined from the system parameters. A variation of the latter is therefore expected to manifest in variation of the the ensemble for each eigenstate and thereby their entanglement aspects. We theoretically analyze the effect of varying system conditions on the eigenstates of a wide range of Hamiltonians and derive a common mathematical formulation for the bipartite entanglement statistics. As the system information in the formulation enters through a single functional of the ensemble parameters, this implies the analogy of statistics for different eigenstate ensembles (non-Haar type) if they share the same complexity parameter and thereby reveals a deep web of connection underlying among quantum states of different Hamiltonians (with same global symmetry class). Besides revealing universality among non-haar states, the information is also relevant for quantum state engineering e.g. how to achieve a near Haar random state starting from a random non-ergodic state.
* Work done in collaboration with my PhD student Devanshu Sekhar
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45125&option_lang=rus
Number: 8
20-Feb-2025 at 4pm Moscow time.
Title of the talk: Broadband variational measurement of a classical force using strongly nondegenerate dichromatic optical pump
Speaker: Prof. S.P. Vyatchanin
Abstract: Maximal sensitivity of classical force detectors utilizing nonlinear opto-mechanical transducers is generally de
fined by the standard quantum limit resulting from the contamination of the detected signal with noncommuting
quantum noises. This restriction can be circumvented by the optimal detection protocols. We here show theo
retically that interrogating a resonant opto-mechanical displacement transducer with a strongly nondegenerate
dichromatic optical probe enables a quantum back-action evading measurement of a classical force acting on the
mechanical oscillator being a part of the opto-mechanical transducer.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45162&option_lang=rus
Number: 9
27-Feb-2025 at 4pm Moscow time.
Title of the talk: Intracavity squeezing as a tool for improving the quantum nondemolition (QND) measurement scheme
Speaker: Daria Salykina
Authors: Dariya Salykina, Stepan Balybin, Farit Ya. Khalili
Abstract: We consider the scheme of quantum nondemolition measurement of optical quanta based on the Kerr nonlinearity in an optical microresonator. We demonstrate that by using the intracavity squeezing of a probe beam it is possible to cancel the interfering effect of self-phase modulation. This results in improvement of scheme sensitivity, allowing it theoretically to approach the single-photon sensitivity. Our estimates show that generation and verification of bright non-Gaussian quantum states with mean photon numbers up to ~1000 is feasible.
Publications:
Balybin S., Salykina D., & Khalili F. Ya. (2023). Improving the sensitivity of Kerr quantum nondemolition measurement via squeezed light. Physical Review A, 108(5), 053708.
Salykina D., Balybin S., Khalili F. Ya. (2025). Intracavity squeezing for a Kerr quantum nondemolition measurement scheme. Physical Review A, 111(1), 013715.
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=45244&option_lang=rus
Number: 10
12-Mar-2025 at 4pm Moscow time.
Title of the talk: Symmetry breaking of counterpropagating Raman waves in optical microresonators: unexpected findings
Speaker: Prof. Elena Anashkina
Authors: Elena Anashkina and Alexey Andrianov
Abstract: Recently, symmetry breaking and related issues in high-Q nonlinear optical microresonators have been of growing interest for fundamental research and photonic device development. Most studies employ Kerr nonlinearity, but this is not the only way. We present our recent results on symmetry breaking of counterpropagating Raman waves at Stokes frequencies in a bidirectionally pumped silica microresonator. We experimentally demonstrate symmetry-broken Raman lasing with previously unreported features such as intensity switching of counterpropagating waves and symmetry restoring during pump frequency sweeping. Symmetric and asymmetric stationary states have been found theoretically, but asymmetric states after a pitchfork bifurcation have proven to be unstable. Such behavior is surprising, since in the case of pure Kerr nonlinearity (without stimulated Raman scattering), a pair of stable asymmetric states is born after a pitchfork bifurcation, and the symmetric solution becomes unstable. The explanation of our experimental findings is based on a weak asymmetry in the scheme, which dramatically changes the dynamic behavior of the system. This is confirmed by numerical simulations with added back reflection for a single Raman wave.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45400&option_lang=rus
Number: 11
19-Mar-2025 at 3:45pm Moscow time.
Title of the talk: Creation and manipulation of Schrödinger cat states based on semiclassical predictions
Speaker: Dr. N.G. Veselkova
Abstract: We consider the generation of Schrödinger cat states using a quantum measurement-induced logical gate where entanglement between the input state of the target oscillator and the Fock state of the ancillary system produced by the quantum non-demolition entangling CZ operation is combined with the homodyne measurement. We utilize the semiclassical approach to construct both the input-output mapping of the field variables in the phase space and the wave function of the output state. This approach is found to predict that the state at the gate output is represented by a minimum disturbed cat-like state which is a superposition of two initial state copies symmetrically displaced by momentum variable. For the target oscillator prepared in the coherent state, we show that the fidelity between the exact solution for the gate output state and the “perfect” Schrödinger cat reconstructed from the semiclassical theory can reach high values exceeding 0.99.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45531&option_lang=rus
Number: 12
28-Mar-2025 at 3pm Moscow time.
Title of the talk: Tomography and Radon transform
Speaker: Dr. V.N. Sivkin
Abstract: Mathematical tomography is a section of mathematics that describes methods for determining the structure of an object using scattering data. Such problems arise in microscopy, medicine, and technical control. In this report, we will write out the basic differential equation of X-ray tomography. In the course of its solution, the Radon transform arises. We will establish a connection between the Fourier transform and the Radon transform, and get acquainted with the methods of its inversion.
Link to the presentation file: www.mathnet.ru/php/seminars.phtml?presentid=45770&option_lang=eng
Number: 13
10-Apr-2025 at 4pm Moscow time.
Title of the talk: On continuous observables in quantum mechanics
Speaker: Dr. D.B. Zotev
Abstract: The theory of continuous observables in quantum mechanics has been arising mistrust among mathematicians. Von Neumann banished from it the delta-function and such exotic entities as "Hermitian product matrices" with continuous indices and quasi-elements in the form of generalized functions. Thanks to von Neumann the paradigm has been spread according to which the state space of a quantum system must only be Hilbert. De'facto he replaced Copenhagen quantum mechanics by a new theory with new physical consequences. In addition, along with the delta-function, quantum mechanics in many ways lost its heuristic power. Dirac brilliantly anticipated the theory of generalized functions and, in fact, there was no need for such a reform. The report presents the theory of continuous observables in the formal form given to it by Heisenberg and Dirac. At the same time, Dirac's approach is strictly formalized within the framework of the theory of generalized functions. But Hilbert spaces are met here too.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45795&option_lang=eng
Number: 14
15-Apr-2025 at 4pm Moscow time.
Title of the talk: Theoretical modelling of superradiant lasers and other open quantum resonant systems
Speaker: Dr. I.E.Protsenko
Authors: I.E.Protsenko and A.V.Uskov
Abstract: An approach for solving the stationary nonlinear quantum Langevin equations for micro-lasers and other small resonant optical devices (for nonlinear optics, plasmonics etc.) is presented. The method uses frequency dependent operators and calculates the mean fluctuation power spectra and photon number. Various approximations for finding analytical expressions are shown. Results for thresholdless lasing, collective Rabi splitting, super-thermal photon statistics and the power increase by the population fluctuations for the superradiant lasers are discussed.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=45951&option_lang=eng
Number: 15
25-Apr-2025 at 4pm Moscow time.
Title of the talk: Optimal sensing of photon addition and subtraction on quantized light
Speaker: Prof. S. Lakshmi Bala
Affiliation: Center of Excellence in Quantum Information, Communication and Computing (CQuICC), IIT Madras, Chennai, India
Abstract: Photon addition to, and subtraction from quantum states of light is of immense current interest, both experimentally and theoretically. We identify a set of markers of photon addition to coherent light and nonclassical single mode states of light such as the squeezed vacuum and the cat states, which are directly computable from relevant optical tomograms. These markers quantify the `distance' between probability density functions corresponding to different states. Examples of such markers are the Wasserstein distance, the Kullback Leibler divergence and the Bhattacharyya distance.
Although the details in the manner in which these markers vary with changes in relevant parameters, depends on the state concerned, they are, in general, sensitive to the underlying interference structures that arise in the tomogram after photon addition/subtraction. Our procedure is universally applicable to the cat and squeezed states, the former displaying the characteristic negativity in its Wigner function, while the latter does not do so. We explicate this in the case of the squeezed vacuum and even coherent states and show that photon addition (or subtraction) is mirrored in the shift in the intensity of specific regions in the tomogram.
In the case of coherent light, the amplification gain due to photon addition, and the dependence of quadrature variances on relevant parameters, are calculated from the tomograms (circumventing state reconstruction), and compared with results obtained (after state reconstruction), in a recent experiment reported in the literature. Our results match well with the fidelity and variance plots obtained by the experimenters.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=46007&option_lang=eng
Number: 16
30-Apr-2025 at 4pm Moscow time.
Title of the talk: Adding or subtracting a single photon is the same, but only for pure squeezed vacuum states
Speaker: Prof. Ray-Kuang Lee
Abstract: The addition of a single photon to a light field can lead to exactly the same outcome as the subtraction of a single photon: starting from the same initial state, both procedures can generate the same final quantum state. We prove that this identity-of-outcome is true for pure squeezed vacuum states of light, and in some sense only for those. We show that mixed states can show this identity-of-outcome for the addition or subtraction of a photon if they are generated from the incoherent sums of pure squeezed vacuum states with the same squeezing. We point out that our results give a reinterpretation to the fact that pure squeezed.
Publication: Ole Steuernagel, Shao-Hua Hu, and Ray-Kuang Lee, APL Quantum 2, 016117 (2025); https://doi.org/10.1063/5.0246230
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=46114&option_lang=eng
Number: 17
27-May-2025 at 4pm Moscow time.
Title of the talk: On Averaging of One-Parameter Semigroups and Their Generators
Speaker: Dr. Rustem Sh. Kalmetev
Abstract: The talk discusses methods for averaging one-parameter semigroups and their generators, focusing on random unbounded operators in Hilbert spaces. Key findings include the construction of generalized expectations through Chernoff equivalence, illustrative examples for resolvent and semigroup averaging, and the role of Feynman formulas in approximating quantum evolution operators. The results highlight the flexibility and limitations of these methods, offering insights into their use in dissipative dynamics, quantization ambiguities, and stochastic differential equations in mathematical physics.
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=46305&option_lang=eng
Number: 18
17-June-2025 at 4:00pm Moscow time.
Title of the talk: Non-Markovian entropy production and its connection to global entanglement in quantum chaos
Speaker: Nataliya S. Arefyeva
Abstract: We focus on the problem of identifying dynamical signatures of quantum behavior, particularly quantum chaos. Recently, we proposed a method for efficiently computing the dynamics of an open quantum system, based on emergent integrals of motion that dynamically form in the environment after a local quench. These integrals carry away the system’s entanglement entropy.
We show that in the Markovian limit, resembling ancilla-based models, entropy production grows linearly and integrable and chaotic behavior are indistinguishable. In contrast, in the non-Markovian regime, entropy production closely follows the Meyer–Wallach global entanglement measure and serves as a sensitive probe of quantum chaos. Thus, we propose non-Markovian entropy production as a marker of quantum chaos.
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=46456&option_lang=eng
Number: 19
7-July-2025 at 4:00pm Moscow time.
Title of the talk: Quantum analog of classical Arnold tongues
Speaker: Artem A. Alexandrov
Abstract: I will review papers by Lee et. al related to synchronization of open quantum systems. Each system is nothing more than a simple harmonic oscillator, interacting with an environment. To start with, I present the essential facts about phase-locking and synchronization in simple dynamical system on torus. Next one will see how does the quantum limit cylce can appear, then we will see how does the classical synchronization domain (Arnold tongue) evolves into its quantum version. The talk is on physical level of rigour.
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=46609&option_lang=rus
Number: 20
17-July-2025 at 3:00pm Moscow time.
Title of the talk: Time-optimal transfer of the quantum state in long qubit arrays
Speaker: Dr. Maxim A. Gorlach
Abstract: Recent technological advances have allowed the fabrication of large arrays of coherently operating coupled qubits, serving as prototypes for quantum processors. However, the optimal control of such systems is notoriously challenging because of the extremely large number of degrees of freedom. The lack of such control limits the potential of large-scale quantum systems.
In this talk, I will discuss a model problem of quantum state transfer in a large nearest-neighbor-coupled qubit array. I will present the optimal control strategy that simultaneously achieves maximal fidelity and minimal transfer time, reaching the quantum speed limit in a lattice with time-varying couplings.
Related paper: https://arxiv.org/abs/2501.11933 , accepted to Physical Review Letters
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=46743&option_lang=rus
Number: 21
25-July-2025 at 4:00pm Moscow time.
Title of the talk: Polaron effect in waveguide quantum optomechanics
Speaker: Prof. Ivan V. Iorsh
Abstract: In my talk I will discuss the impact of the quantized mechanical motion of optically trapped atoms, arranged in proximity to a one-dimensional waveguide, on the propagation of polariton modes. Our study identifies a regime of resonant phonon-assisted mixing between lower and upper polaritons, resulting in a pronounced polaron effect. This effect is characterized by the formation of new band gaps and the appearance of weakly dispersive states within the original polariton band gap. The polaron spectrum, which can be directly probed via resonant elastic scattering, provides novel opportunities for quantum optical applications. These findings open avenues for enhanced control in state-of-the-art waveguide quantum electrodynamics experiments with cold atoms.
Related paper: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.111.155424
Link to the video recording: https://www.mathnet.ru/php/seminars.phtml?presentid=46897&option_lang=rus
Number: 22
28-July-2025 at 4:00pm Moscow time.
Title of the talk: Josephson “flying qubit” revival: Flux-based control optimization
Speaker: Dr. Marina V. Bastrakova
Abstract: A decade ago, Josephson “flying qubits” based on adiabatic superconducting logic cells showed promise as quantum data buses, but their development stalled due to the incompatibility of traditional qubit control methods with their design. We revisit this concept by exploring the control of the inductively shunted two-junction superconducting interferometer (adiabatic quantum flux parametron, AQFP) in the quantum regime using unipolar magnetic field pulses generated by adiabatic superconducting electronics. Our research demonstrates the feasibility of high fidelity quantum operations (fidelity more than 99.99%) in this system via Landau–Zener tunneling. To this end, a method is proposed for selecting the duration and shape of control pulses to eliminate unwanted leakage into high-lying states in AQFP-based systems.
Related paper: https://www.sciencedirect.com/science/article/pii/S0960077925003662
Link to the video recording: will appear soon!
Number: 23
6-Aug-2025 at 4:00pm Moscow time.
Title of the talk: Projection approach for composite open quantum systems
Speaker: Artem Yu. Karasev
Abstract: This report presents the application of the Nakajima–Zwanzig projection method to the derivation of kinetic equations for systems treated as weakly interacting open subsystems. As illustrative examples, we analyze the Jaynes–Cummings model with dissipation and the spontaneous parametric down-conversion model involving two dissipative modes. For both systems, the approach enables a systematic derivation of corrections to the parametric approximation by accounting for quantum depletion of the pumping field.
Link to the video recording: www.mathnet.ru/php/seminars.phtml?presentid=46931&option_lang=rus
Number: 24
27-Aug-2025 at 4:00pm Moscow time.
Title of the talk: Some Practical Problems of Quantum Gate Teleportation (QGT)
Speaker: Dr. Sergey S. Sysoev, Department of software engineering, SPBU
Abstract: Quantum teleportation is unquestionably an important resource, especially in the one-way computation model. However, we will focus on the circuit-based model and explore what this technique can contribute to its toolset. Quantum algorithms can benefit from teleportation if we teleport gates rather than states. This idea was investigated two decades ago by Gottesman and Chuang, whose paper optimistically claimed that teleportation is a universal computational resource. Apart from teleporting the CX gate within the KLM protocol, though, it is hard to find convincing practical uses for this technique. Furthermore, the derivation of the CX-gate procedure itself was never fully clarified. In this talk we will revisit their method, extend it to the Toffoli gate, offer fresh motivation for pursuing gate teleportation, and identify the obstacles encountered along the way.
Plan of the talk:
1. Why we want a universal QGT procedure (spoiler: for parallel quantum computing)
2. Understanding QGT for single-qubit gates—any issues? (yes, several)
3. QGT for the CX gate—does it actually work? (more or less)
4. QGT for the Toffoli gate
5. Teleportation of several gates in a row
Link to the video recording: www.mathnet.ru/rus/present47059
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Organizers of the seminar:
Ranjit Singh, Independent Researcher, Moscow, Russia
Alexander E. Teretenkov, Senior Scientific Researcher, Department of Mathematical Methods for Quantum Technologies, Steklov Mathematical Institute of Russian Academy of Sciences, Moscow, Russia
Link to join Telegram channel Quantum optics and related topics (QOART):
https://t.me/+i6rnhM_Wp1YwY2Ji
Topics of the seminar
Quantum linear and nonlinear optics
Nonlinear processes (e.g., parametric down-conversion and others) in bulk and periodically poled nonlinear crystals
Quantum linear and nonlinear interferometers
Generation of non-Gaussian states (e.g., Schrödinger cat states, Fock states, states having negative Wigner function)
Propagation of photons in free space
Quantum information processing with continuous variables
Quantum correlations
Quantum entanglement
Quantum imaging
Polarization of light (in Quantum and Nonlinear Optics)
Quantum photonics
Optical quantum sensing
Quantum optical metrology
Quantum measurement
Related topics:
Open quantum systems
Quantum cryptography
Quantum tomography
Quantum teleportation
Quantum control
Quantum computing
Quantum information
Quantum optomechanics
Quantum technology
Language:
We encourage speakers to prepare slides in English.
If there is a non-Russian-speaking participant in the room and the speaker is ready to speak in English, then the talk will be in English.