arXiv subjects

O. V. Astafiev

Publications and source records attributed to O. V. Astafiev.

At least 19 recordsLinked to original sources

arXiv2026

Sideband fingerprints of antibunched light in cascaded quantum wave mixing

Quantum wave mixing on a single superconducting qubit produces a hierarchy of coherent side peaks associated with elastic multiphoton scattering pathways. In a cascaded source--probe geometry these pathways become sensitive to the photon statistics of the radiation emitted by the source qubit. We develop an analytical theory of this effect starting from the cascaded master equation in the weak-driving regime. In the coherent-filtering limit $γ_{\rm s}\ggγ_{\rm pr}$, the standard coherent--coherent wave-mixing hierarchy is recovered. In the opposite limit $γ_{\rm pr}\ggγ_{\rm s}$, side peaks associated with multiphoton absorption from the antibunched source field are parametrically suppressed. Numerical solutions confirm the analytical scaling laws. The resulting sideband hierarchy provides a frequency-domain fingerprint of antibunched itinerant microwave light.

quant-ph↗

arXiv2026

Photon pairs, squeezed light and the quantum wave mixing effect in a cascaded qubit system

We develop a theoretical description of quantum wave mixing (QWM) in a cascaded waveguide-QED system of two superconducting qubits, where the probe is driven by an external coherent tone and by the resonance fluorescence of a strongly driven source qubit. Starting from the field correlation functions of the source emission, we derive an effective master-equation treatment for the probe and identify the regime in which the incident fluorescence is characterized by anomalous correlations. When the coherent Rayleigh component of the source spectrum is suppressed, the probe equations of motion become equivalent to those for a qubit driven by a coherent tone and broadband squeezed light. This equivalence implies a selection rule for the peaks of the QWM spectrum, with a strong suppression of sidebands associated with processes involving an odd number of photons taken from the source field. Numerical simulations of the full cascaded two-qubit model for different ratios of radiative decay rates unambiguously confirm the participation of correlated photon pairs in QWM processes. The current research illustrates that the analysis of peak amplitudes can be used to probe photon statistics in the incident nonclassical field.

quant-ph↗

arXiv2026

Aharonov-Casher Effect and the Coherent Flux Tunneling in the Hybrid Charge Quantum Interference Device

By exploiting the Aharonov-Casher effect we demonstrate a suppression of magnetic flux tunneling in a Hybrid Charge Quantum Interference Device. The main part of this device is two Josephson junctions with a small superconducting island between them. To minimize phase fluctuations across Josephson junctions, this structure is embedded in a compact super-inductive NbN loop. The Interference between the flux tunneling paths is determined by the island-induced charge, which is controlled by an external voltage. The charge sensitive operation of the device is subjected to poisoning by the quasiparticles generated in the NbN film.

cond-mat.supr-con↗

arXiv2024

Direct experimental observation of sub-poissonian photon statistics by means of multi-photon scattering on a two-level system

A cascade of two-level superconducting artificial atoms -- a source and a probe -- strongly coupled to a semi-infinite waveguide is a promising tool for observing nontrivial phenomena in quantum nonlinear optics. The probe atom can scatter an antibunched radiation emitted from the source, thereby generating a field with specific properties. We experimentally demonstrate wave mixing between nonclassical light from the coherently cw-pumped source and another coherent wave acting on the probe. We observe unique features in the wave mixing stationary spectrum which differs from mixing spectrum of two classical waves on the probe. These features are well described by adapting the theory for a strongly coupled cascaded system of two atoms. We further analyze the theory to predict non-classical mixing spectra for various ratios of atoms' radiative constants. Both experimental and numerical results confirm the domination of multi-photon scattering process with only a single photon from the source. We evaluate entanglement of atoms in the quasistationary state and illustrate the connection between the expected second-order correlation function of source's field and wave mixing side peaks corresponding to a certain number of scattered photons.

quant-ph↗

arXiv2024

Dynamics and Resonance Fluorescence from a Superconducting Artificial Atom Doubly Driven by Quantized and Classical Fields

We report an experimental demonstration of resonance fluorescence in a two-level superconducting artificial atom under two driving fields coupled to a detuned cavity. One of the fields is classical and the other is varied from quantum (vacuum fluctuations) to classical one by controlling the photon number inside the cavity. The device consists of a transmon qubit strongly coupled to a one-dimensional transmission line and a coplanar waveguide resonator. We observe a sideband anti-crossing and asymmetry in the emission spectra of the system through a one-dimensional transmission line, which is fundamentally different from the weak coupling case. By changing the photon number inside the cavity, the emission spectrum of our doubly driven system approaches to the case when the atom is driven by two classical bichromatic fields. We also measure the dynamical evolution of the system through the transmission line and study the properties of the first-order correlation function, Rabi oscillations and energy relaxation in the system. The study of resonance fluorescence from an atom driven by two fields promotes understanding decoherence in superconducting quantum circuits and may find applications in superconducting quantum computing and quantum networks.

quant-ph↗

arXiv2023

Evolution of coherent waves driving a single artificial atom

An electromagnetic wave propagating through a waveguide with a strongly coupled superconducting artificial two-level atom exhibits an evolving superposition with the atom. The Rabi oscillations in the atom result from a single excitation-relaxation, corresponding to photon absorption and stimulated emission from/to the field. In this study, we investigate the time-dependent behavior of the transmitted field and extract its spectra. The scattered fields are described using input-output theory. We demonstrate that the time evolution of the propagating fields, due to interaction, encapsulates all information about the atom. Additionally, we deduce the dynamics of the incoherent radiation component from the measured first-order correlation function of the field.

quant-ph↗

arXiv2023

Quantum theory of wave mixing on a two-level system

We apply the scattering matrix formalism to wave mixing on a quantum two-level system. We carry out the fermionization of the two-level system degrees of freedom using the Popov-Fedotov semions, calculate n-particle Green's function, and apply the Lehmann-Symanzik-Zimmermannn reduction procedure. Using the developed approach, we provide a consistent quantum explanation of the appearance of coherent side peaks observed in an experiment on the scattering of bichromatic radiation on a two-level artificial atom \cite{dmitriev2019probing}. We show that the spectrum observed in the experiment is the result of bosonic stimulated scattering of photons from one mode of the bichromatic drive to another and vice versa.

quant-ph↗

arXiv2022

Overcoming photon blockade in circuit QED single-atom maser with engineered metastability and strong coupling

Reaching high cavity population with a coherent pump in the strong-coupling regime of a single-atom laser is impossible due to the photon blockade effect. In this work, we experimentally demonstrate that in a single-atom maser based on a transmon strongly coupled to two resonators it is possible to pump over a dozen of photons into the system. The first high-quality resonator plays a role of usual lasing cavity, and the second one presents a controlled dissipation channel, bolstering population inversion, and modifies the energy level structure to lift the blockade. As a confirmation of lasing action, we observe conventional laser features such as the narrowing of emission linewidth and external signal amplification. Additionally, we report unique single-atom features: self-quenching and several lasing thresholds.

quant-ph↗

arXiv2022

Quantized current steps due to the a.c. coherent quantum phase-slip effect

The AC Josephson effect predicted in 1962 and observed experimentally in 1963 as quantised voltage steps (the Shapiro steps) from photon assisted tunnelling of Cooper pairs is among the most fundamental phenomena of quantum mechanics and is vital for metrological quantum voltage standards. The physically dual effect, the AC coherent quantum phase slip (CQPS), photon assisted tunnelling of magnetic fluxes through a superconducting nanowire, is envisaged to reveal itself as quantised current steps. The basic physical significance of the AC CQPS is also complemented by practical importance in future current standards; a missing element for closing the Quantum Metrology Triangle. In 2012, the CQPS was demonstrated as superposition of magnetic flux quanta in superconducting nanowires. However the direct sharp current steps in superconductors; the only unavailable basic effect of superconductivity to date, was unattainable due to lack of appropriate materials and challenges in circuit engineering. Here we report the direct observation of the dual Shapiro steps in a superconducting nanowire. The sharp steps are clear up to 26 GHz frequency with current values 8.3 nA and limited by the present setup bandwidth. The current steps have been theoretically predicted in small Josephson junctions (JJs) 30 years ago. However, broadening unavoidable in JJs prevents their direct experimental observation. We solve this problem by placing a thin NbN nanowire in an inductive environment.

cond-mat.supr-con↗

arXiv2022

Time dynamics of multi-photon scattering in a two-level mixer

A superconducting qubit in a waveguide behaves as a point-like nonlinear element. If irradiated with nearly resonant microwave pulses, the qubit undergoes quantum evolution and generates coherent fields at sideband frequencies due to elastic scattering. This effect is called Quantum Wave Mixing (QWM), and the number of emerged side components depends on the number of interacting photons. By driving a superconducting qubit with short pulses with alternating carrier frequencies, we control the maximal number of photons simultaneously interacting with a two-level system by varying the number and duration of applied pulses. Increasing the number of pulses results in consecutive growth of the order of non-linearity, which manifests in additional coherent side peaks appearing in the spectrum of scattered radiation while the whole spectrum maintains its asymmetry.

quant-ph↗

arXiv2021

Effects of photon statistics in wave mixing on a single qubit

We theoretically consider wave mixing under the irradiation of a single qubit by two photon fields. The first signal is a classical monochromatic drive, while the second one is a nonclassical light. Particularly, we address two examples of a nonclassical light: (i) a broadband squeezed light and (ii) a periodically excited quantum superposition of Fock states with 0 and 1 photons. The mixing of classical and nonclassical photon fields gives rise to side peaks due to the elastic multiphoton scattering. We show that side peaks structure is distinct from the situation when two classical fields are mixed. The most striking feature is that some peaks are absent. The analysis of peak amplitudes can be used to probe photon statistics in the nonclassical mode.

quant-ph↗

arXiv2020

Single-atom maser with engineered circuit for population inversion

We present a blueprint for a maser with a single three-level transmon superconducting artificial atom. The system can be pumped coherently via a two-photon process, and to achieve high population inversion, the relaxation rate of the metastable state is increased via an auxiliary low-Q cavity coupled to a transition between the transmon excited states. We show numerically that such a maser can operate both in the intermediate coupling regime with super-Poissonian photon statistics and in the strong coupling regime, where the statistics is sub-Poissonian. For the former, the maser exhibits thresholdless behavior and for the latter, there is a well-defined pumping threshold. A useful side-effect of the auxiliary resonator is that it allows to overcome the photon blockade effect for the pump, which would otherwise prevent high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.

quant-ph↗

arXiv2020

Photon transport in a Bose-Hubbard chain of superconducting artificial atoms

We demonstrate non-equilibrium steady-state photon transport through a chain of five coupled artificial atoms simulating the driven-dissipative Bose-Hubbard model. Using transmission spectroscopy, we show that the system retains many-particle coherence despite being coupled strongly to two open spaces. We show that system energy bands may be visualized with high contrast using cross-Kerr interaction. For vanishing disorder, we observe the transition of the system from the linear to the nonlinear regime of photon blockade in excellent agreement with the input-output theory. Finally, we show how controllable disorder introduced to the system suppresses this non-local photon transmission. We argue that proposed architecture may be applied to analog simulation of many-body Floquet dynamics with even larger arrays of artificial atoms paving an alternative way to demonstration of quantum supremacy

quant-ph↗

arXiv2020

Light-dressing of a diatomic superconducting artificial molecule

In this work, we irradiate a superconducting artificial molecule composed of two coupled tunable transmons with microwave light while monitoring its state via joint dispersive readout. Performing high-power spectroscopy, we observe and identify a variety of single- and multiphoton transitions. We also find that at certain fluxes, the measured spectrum of the system deviates significantly from the solution of the stationary Schrödinger equation with no driving. We reproduce these unusual spectral features by solving numerically the full master equation for a steady-state and attribute them to an Autler-Townes-like effect in which a single tone is simultaneously dressing the system and probing the transitions between new eigenstates. We show that it is possible to find analytically the exact frequencies at which the satellite spectral lines appear by solving self-consistent equations in the rotating frame. Our approach agrees well with both the experiment and the numerical simulation.

physics.atom-ph↗

arXiv2020

Two-level system as a quantum sensor of absolute power

A two-level quantum system can absorb or emit not more than one photon at a time. Using this fundamental property, we demonstrate how a superconducting quantum system strongly coupled to a transmission line can be used as a sensor of the photon flux. We propose four methods of sensing the photon flux and analyse them for the absolute calibration of power by measuring spectra of scattered radiation from the two-level system. This type of sensor can be tuned to operate in a wide frequency range, and does not disturb the propagating waves when not in use. Using a two-level system as a power sensor enables a range of applications in quantum technologies, here in particular applied to calibrate the attenuation of transmission lines inside dilution refrigerators.

quant-ph↗

arXiv2019

Tunable Microwave Single-photon Source Based on Transmon Qubit with High Efficiency

Single-photon sources are of great interest because they are key elements in different promising applications of quantum technologies. Here we demonstrate a highly efficient tunable on-demand microwave single-photon source based on a transmon qubit with the intrinsic emission efficiency above 98$\%$. The high efficiency ensures a negligible pure dephasing rate and the necessary condition for generation of indistinguishable photons. We provide an extended discussion and analysis of the efficiency of the photon generation. To further experimentally confirm the single-photon property of the source, correlation functions of the emission field are also measured using linear detectors with a GPU-enhanced signal processing technique. Our results experimentally demonstrate that frequency tunability and negligible pure dephasing rate can be achieved simultaneously and show that such a tunable single-photon source can be good for various practical applications in quantum communication, simulations and information processing in the microwave regime.

quant-ph↗

arXiv2018

Probing the statistics of coherent states by continuous wave mixing on a single artificial atom

We study four- and higher-order wave mixing of continuous coherent waves on a single superconducting artificial atom. Narrow side peaks of different orders of nonlinearity resulting from elastic multi-photon scattering on the atom are observed and investigated. We derive an analytical expression for the peak amplitudes and show that the ratio of any two adjacent peaks is a function of driving amplitudes and detuning. This is attributed to the photon distribution in the coherent states and provides a measure for characterisation of photon statistics in non-classical coherent waves. We also demonstrate an Autler-Townes-like splitting of side peaks, the magnitude of which scales with the scattering order.

quant-ph↗

arXiv2017

Experimental demonstration of a two-dimensional phonon cavity in the quantum regime

The quantum regime in acoustic systems is a focus of recent fundamental research in the new field of Quantum Acoustodynamics (QAD). Systems based on surface acoustic waves having an advantage of easy integration in two-dimensions are particularly promising for the demonstration of novel effects in QAD and development of novel devices of quantum acousto-electronics. We demonstrate the vacuum mode of the surface acoustic wave resonator by coupling it to a superconducting artificial atom. The artificial atom is implemented into the resonator formed by two Brag mirrors. The results are consistent with expectations supported by the system model and our calculations. This work opens the way to map analogues of quantum optical effects into acoustic systems.

quant-ph↗