arXiv subjects

D. S. Smirnov

Publications and source records attributed to D. S. Smirnov.

At least 37 records · Page 2Linked to original sources

arXiv2023

Evidencing the squeezed dark nuclear spin state in lead halide perovskites

Coherent many-body states are highly promising for robust and scalable quantum information processing. While far-reaching theoretical predictions have been made for various implementations, direct experimental evidence of their appealing properties can be challenging. Here, we demonstrate coherent optical manipulation of the nuclear spin ensemble in the lead halide perovskite semiconductor FAPbBr$_3$ (FA=formamidinium), targeting a long-postulated collective dark state that is insensitive to optical pumping. Via optical orientation of localized hole spins we drive the nuclear many-body system into an entangled state, requiring a weak magnetic field of only a few Millitesla strength at cryogenic temperatures. During its fast build-up, the nuclear polarization along the optical axis remains small, while the transverse nuclear spin fluctuations are strongly reduced, corresponding to spin squeezing as evidenced by a strong violation of the generalized nuclear squeezing-inequality with $ξ_s < 0.3$. The dark state evidenced in this process corresponds to an approximately 750-body entanglement between the nuclei. Dark nuclear spin states can be exploited to store quantum information benefiting from their long-lived many-body coherence and to perform quantum measurements with a precision beyond the standard limit.

cond-mat.mtrl-sci↗

arXiv2022

Tuning the nuclei-induced spin relaxation of localized electrons by the quantum Zeno and anti-Zeno effects

Quantum measurement back action is fundamentally unavoidable when manipulating electron spins. Here we demonstrate that this back action can be efficiently exploited to tune the spin relaxation of localized electrons induced by the hyperfine interaction. In optical pump-probe experiments, powerful probe pulses suppress the spin relaxation of electrons on Si donors in an InGaAs epilayer due to the quantum Zeno effect. By contrast, an increase of the probe power leads to a speed up of the spin relaxation for electrons in InGaAs quantum dots due to the quantum anti-Zeno effect. The microscopic description shows that the transition between the two regimes occurs when the spin dephasing time is comparable to the probe pulse repetition period.

cond-mat.mes-hall↗

arXiv2022

Valley-magnetophonon resonance for interlayer excitons

Heterobilayers consisting of MoSe$_2$ and WSe$_2$ monolayers can host optically bright interlayer excitons with intriguing properties such as ultralong lifetimes and pronounced circular polarization of their photoluminescence due to valley polarization, which can be induced by circularly polarized excitation or applied magnetic fields. Here, we report on the observation of an intrinsic valley-magnetophonon resonance for localized interlayer excitons promoted by invervalley hole scattering. It leads to a resonant increase of the photoluminescence polarization degree at the same field of 24.2 Tesla for H-type and R-type stacking configurations despite their vastly different excitonic energy splittings. As a microscopic mechanism of the hole intervalley scattering we identify the scattering with chiral TA phonons of MoSe$_2$ between excitonic states mixed by the long-range electron hole exchange interaction.

cond-mat.mes-hall↗

arXiv2022

Optical measurement of electron spins in quantum dots: Quantum Zeno effects

We describe the effects of the quantum back action under continuous optical measurement of electron spins in quantum dots. We consider the system excitation by elliptically polarized light close to the trion resonance, which allows for the simultaneous spin orientation and measurement. We microscopically demonstrate that the nuclei-induced spin relaxation can be both suppressed and accelerated by the continuous spin measurement due to the quantum Zeno and anti-Zeno effects, respectively. Our theoretical predictions can be directly compared with the future experimental results and straightforwardly generalized for the pump-probe experiments.

cond-mat.mes-hall↗

arXiv2022

Spin noise in birefringent and inhomogeneous media

It is known that linear birefringence of the medium essentially hinders measuring the Faraday effect. For this reason, optically anisotropic materials have never been considered as objects of the Faraday-rotation-based spin noise spectroscopy (SNS). We show, both theoretically and experimentally, that strong optical anisotropy that may badly suppress the regular Faraday rotation of the medium, practically does not affect the measurement of the spatially uncorrelated spin fluctuations. An important consequence of this result is that the Faraday-rotation noise should be also insensitive to spatially nonuniform birefringence, which makes the SNS applicable to a wide class of optically anisotropic and inhomogeneous materials. We also show that the birefringent media provide additional opportunity to measure spatial spin correlations. Results of the experimental measurements of the spin-noise spectra performed on 4$f$--4$f$ transitions of Nd$^{3+}$ ions in the CaWO$_4$ and LiYF$_4$ crystals well agree with the theory.

cond-mat.mes-hall↗

arXiv2021

Nuclear spin dynamics and noise in anisotropic large box model

We consider the central spin model in the box approximation taking into account external magnetic field and anisotropy of the hyperfine interaction. From the exact Hamiltonian diagonalization we obtain analytical expressions for the nuclear spin dynamics in the limit of many nuclear spins. We predict the nuclear spin precession in zero magnetic field for the case of anisotropic interaction between electron and nuclear spins. We calculate and describe the nuclear spin noise spectra in the thermodynamic equilibrium. The obtained results can be used for the analysis of the nuclear spin induced current fluctuations in organic semiconductors.

cond-mat.mes-hall↗

arXiv2021

Dynamic Valley Polarization in Moire Quantum Dots

We describe the effects of the crossing of the exciton levels in moire quantum dots in external magnetic field. We demonstrate that the unpolarized light can create significant dynamic valley polarization of interlayer excitons in the conditions where the Zeeman energy is much smaller than the thermal energy. The angular momentum is gained by the excitons from the nuclear spin fluctuations. In the $n$-type moire quantum dots for the typical experimental parameters, the unpolarized light can lead to the complete valley polarization of the resident electrons.

cond-mat.mes-hall↗

arXiv2021

Current Induced Hole Spin Polarization in Quantum Dot via Chiral Quasi Bound State

We put forward a mechanism for current induced spin polarization for a hole in a quantum dot side-coupled to a quantum wire, that is based on the spin-orbit splitting of the valence band. We predict that in a stark contrast with the traditional mechanisms based on the linear in momentum spin-orbit coupling, an exponentially small bias applied to the quantum wire with heavy holes is enough to create the 100% spin polarization of a localized light hole. Microscopically, the effect is related with the formation of chiral quasi bound states and the spin dependent tunneling of holes from the quantum wire to the quantum dot. This novel current induced spin polarization mechanism is equally relevant for the GaAs, Si and Ge based semiconductor nanostructures.

cond-mat.mes-hall↗

arXiv2021

Dynamic polarization of electron spins in indirect band gap (In,Al)As/AlAs quantum dots in weak magnetic field: experiment and theory

A novel spin orientation mechanism - dynamic electron spin polarization has been recently suggested in Phys. Rev. Lett. $\mathbf{125}$, 156801 (2020). It takes place for unpolarized optical excitation in weak magnetic fields of the order of a few millitesla. In this paper we demonstrate experimentally and theoretically that the dynamic electron spin polarization degree changes sign as a function of time, strength of the applied magnetic field and its direction. The studies are performed on indirect band-gap (In,Al)As/AlAs quantum dots and their results are explained in the framework of a theoretical model developed for our experimental setting.

cond-mat.mes-hall↗

arXiv2021

Resonant spin amplification in Faraday geometry

We demonstrate the realization of the resonant spin amplification (RSA) effect in Faraday geometry where a magnetic field is applied parallel to the optically induced spin polarization so that no RSA is expected. However, model considerations predict that it can be realized for a central spin interacting with a fluctuating spin environment. As a demonstrator, we choose an ensemble of singly-charged (In,Ga)As/GaAs quantum dots, where the resident electron spins interact with the surrounding nuclear spins. The observation of RSA in Faraday geometry requires intense pump pulses with a high repetition rate and can be enhanced by means of the spin-inertia effect. Potentially, it provides the most direct and reliable tool to measure the longitudinal $g$ factor of the charge carriers.

cond-mat.mes-hall↗

arXiv2021

Nuclear spin dynamics, noise, squeezing and entanglement in box model

We obtain a compact analytical solution for the nonlinear equation for the nuclear spin dynamics in the central spin box model in the limit of many nuclear spins. The total nuclear spin component along the external magnetic field is conserved and the two perpendicular components precess or oscillate depending on the electron spin polarization, with the frequency, determined by the nuclear spin polarization. As applications of our solution, we calculate the nuclear spin noise spectrum and describe the effects of nuclear spin squeezing and many body entanglement in the absence of a system excitation.

cond-mat.mes-hall↗

arXiv2020

Electric current noise in mesoscopic organic semiconductors

We demonstrate that nuclear spin fluctuations lead to the electric current noise in the mesoscopic samples of organic semiconductors showing the pronounced magnetoresistance in weak fields. For the bipolaron and electron-hole mechanisms of organic magnetoresistance, the current noise spectrum consists of the high frequency peak related to the nuclear spin precession in the Knight field of the charge carriers and the low frequency peak related to the nuclear spin relaxation. The shape of the spectrum depends on the external magnetic and radiofrequency fields, which allows one to prove the role of nuclei in magnetoresistance experimentally.

cond-mat.mes-hall↗

arXiv2020

Theory of optically detected spin noise in nanosystems

Theory of spin noise in low dimensional systems and bulk semiconductors is reviewed. Spin noise is usually detected by optical means, continuously measuring the rotation angle of the polarization plane of the probe beam passing through the sample. Spin noise spectra yield rich information about the spin properties of the system including, for example, $g$-factors of the charge carriers, spin relaxation times, parameters of the hyperfine interaction, spin-orbit interaction constants, frequencies and widths of the optical resonances. The review describes basic models of spin noise, methods of its theoretical description, and their relation with the experimental results. We also discuss the relation between the spin noise spectroscopy, the strong and weak quantum measurements and the spin flip Raman scattering, and analyze similar effects including manifestations of the charge, current and valley polarization fluctuations in the optical response. Possible directions for further development of the spin noise spectroscopy are outlined.

cond-mat.mes-hall↗

arXiv2020

Spin polarization recovery and Hanle effect for charge carriers interacting with nuclear spins in semiconductors

We report on theoretical and experimental study of the spin polarization recovery and Hanle effect for the charge carriers interacting with the fluctuating nuclear spins in the semiconductor structures. We start the theoretical description from the simplest model of static and isotropic nuclear spin fluctuations. Then we describe the modification of the polarization recovery and Hanle curves due to the anisotropy of the hyperfine interaction, finite nuclear spin correlation time, and the strong pulsed spin excitation. For the latter case, we describe the resonance spin amplification effect in the Faraday geometry and discuss the manifestations of the quantum Zeno effect. The set of the experimental results for various structures and experimental conditions is chosen to highlight the specific effects predicted theoretically. We show that the spin polarization recovery is a very valuable tool for addressing carrier spin dynamics in semiconductors and their nanostructures.

cond-mat.mes-hall↗

arXiv2020

Quantum Zeno effect under continuous spin noise measurement in a quantum dot-micropillar cavity

We theoretically describe the quantum Zeno effect in a spin-photon interface represented by a charged quantum dot in a micropillar cavity. The electron spin in this system entangles with the polarization of the transmitted photons, and their continuous detection leads to the slowing of the electron spin precession in external magnetic field and induces the spin relaxation. We obtain a microscopic expression for the spin measurement rate and calculate the second and fourth order correlation functions of the spin noise, which evidence the change of the spin statistics due to the quantum Zeno effect. We demonstrate, that the quantum limit for the spin measurement can be reached for any probe frequency using the homodyne nondemolition spin measurement, which maximizes the rate of the quantum information gain.

cond-mat.mes-hall↗

arXiv2020

Dynamic polarization of electron spins interacting with nuclei in semiconductor nanostructures

We suggest a new spin orientation mechanism for localized electrons: $dynamic~electron~spin~polarization~provided~by~nuclear~spin~fluctuations$. The angular momentum for the electrons is gained from the nuclear spin system via the hyperfine interaction in a weak magnetic field. For this the sample is illuminated by an unpolarized light, which directly polarizes neither the electrons nor the nuclei. We predict, that for the electrons bound in localized excitons 100% spin polarization can be reached in longitudinal magnetic fields of a few millitesla. The proof of principle experiment is performed on momentum-indirect excitons in (In,Al)As/AlAs quantum dots, where in a magnetic field of 17 mT the electron spin polarization of 30% is measured.

cond-mat.mes-hall↗

arXiv2020

Exciton energy oscillations induced by quantum beats

In this paper, we experimentally demonstrate an oscillating energy shift of quantum-confined exciton levels in a semiconductor quantum well after excitation into a superposition of two quantum confined exciton states of different parity. Oscillations are observed at frequencies corresponding to the quantum beats between these states. We show that the observed effect is a manifestation of the exciton density oscillations in the real space similar to the dynamics of a Hertzian dipole. The effect is caused by the exciton-exciton exchange interaction and appears only if the excitons are in a superposition quantum state. Thus, we have found clear evidence for the incoherent exchange interaction in the coherent process of quantum beats. This effect may be harnessed for quantum technologies requiring the quantum coherence of states.

cond-mat.mes-hall↗

arXiv2020

Optical Resonance Shift Spin Noise Spectroscopy

Quantum spin fluctuations provide a unique way to study spin dynamics without system perturbation. Here we put forward an optical resonance shift spin noise spectroscopy as a powerful tool to measure the spin noise of various systems from magnetic impurities in solids to free atoms and molecules. The quantum spin fluctuations in these systems can shift the optical resonances by more than the homogeneous linewidth and produce huge Faraday rotation noise. We demonstrate, that the resonance shift spin noise spectroscopy gives access to the high order spin correlators, which contain complete information about the spin dynamics in contrast with the second order correlator measured by conventional Pauli-blocking spin noise spectroscopy. The high order quantum spin correlators manifest themselves as a comb of peaks in the Faraday rotation noise spectra in transverse magnetic field. This effect is closely related with the multispin flip Raman scattering observed in the Mn-doped nanostructures.

cond-mat.mes-hall↗