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arXiv:2601.20768

Millisecond spin coherence of electrons in semiconducting perovskites revealed by spin mode locking

Sergey R. Meliakov, Evgeny A. Zhukov, Vasilii V. Belykh, Dmitri R. Yakovlev, Bekir Turedi, Maksym V. Kovalenko, Manfred Bayer

cond-mat.mtrl-sciquant-phSubmitted Jan 28, 2026• Announced Jan 29, 2026
arXivHTMLPDF

Abstract

Long spin coherence times of carriers are essential for implementing quantum technologies using semiconductor devices for which, however, a possible obstacle is spin relaxation. For the spin dynamics, decisive features are the band structure, crystal symmetry, and quantum confinement. Perovskite semiconductors recently have come into focus of studies of their spin states, notivated by efficient optical access and potentially long-living coherence. Here, we report an electron spin coherence time $T_2$ of the order of 1 ms, measured for a bulk FA$_{0.95}$Cs$_{0.05}$PbI$_3$ lead halide perovskite crystal. Using periodic laser pulses, we synchronize the electron spin Larmor precession about an external magnetic field in an inhomogeneous ensemble, the effect known as spin mode locking. It appears as a decay of the optically created ensemble spin polarization within the dephasing time $T_2^*$ of up to 20 ns and its revival during the spin coherence time $T_2$ reaching the millisecond range. This exceptionally long spin coherence time in a bulk crystal is complemented by millisecond-long longitudinal spin relaxation times $T_1$ for electrons and holes, measured by optically-detected magnetic resonance. These long-lasting spin dynamics highlight perovskites as promising platform for the quantum devices with all-optical control.

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Millisecond spin relaxation times of distinct electron and hole subensembles in MA$_x$FA$_{1-x}$PbI$_3$ perovskite crystals

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The unique combination of outstanding optical quality and attractive spin properties opens new avenues for optical spin control in hybrid organic-inorganic perovskite semiconductors. Using the optically detected magnetic resonance technique, we study the spins of electrons and holes in mixed-cation MA$_x$FA$_{1-x}$PbI$_3$ single crystals with $x = 0.4$ and 0.8. Multiple distinct spin subensembles with $g$-factors spanning from 2.9 to 3.6 for electrons and from 0.5 to 1.2 for holes are resolved, revealing diverse localization environments. We measure the longitudinal spin relaxation times, $T_1$, reaching 2 ms and remaining in the $μ$s range even for weakly localized carriers at the cryogenic temperature of 1.6 K. The magnetic-field dependence of $T_1$ is dominated by the random nuclear (Overhauser) fields with strengths of $\sim 0.4-0.8$ mT for electrons and $\sim 4-12$ mT for holes, corresponding to $μ$s-long correlation times of the hyperfine field determined by carrier hopping between shallow localization sites. The temperature dependence of $T_1$ reveals a weak localization potential of the charge carriers and shows a correlation between $T_1$ and the inhomogeneity of the spin ensemble. These results establish mixed-A-site perovskite single crystals as a promising solid-state platform with long-lived spin states for quantum information applications.

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The coherent spin dynamics of resident carriers, electrons, and holes in semiconductor nanostructures is studied theoretically under the conditions of periodical optical excitation using short laser pulses and in an external magnetic field. The generation and dephasing of spin polarization in an ensemble of carrier spins, for which the relaxation time of individual spins exceeds the repetition period of the laser pulses, are analyzed. Accumulation of the spin polarization is manifested either as resonant spin amplification or as mode locking of carrier spin coherences. It is shown that both regimes have the same origin, while their appearance is determined by the optical pump power and the spread of spin precession frequencies in the ensemble.

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The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study 3-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with $T_ 2$ = 0.45 ns which is determined by the radiative lifetime of trions $T_1$ = 0.27 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons $T_{2,e}$ ~ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.

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Long spin coherence times of carriers are essential for implementing quantum technologies using semiconductor devices for which, however, a possible obstacle is spin relaxation. For the spin dynamics, decisive features are the band structure, crystal symmetry, and quantum confinement. Perovskite semiconductors recently have come into focus of studies of their spin states, notivated by efficient optical access and potentially long-living coherence. Here, we report an electron spin coherence time T2T_2T2​ of the order of 1 ms, measured for a bulk FA0.95_{0.95}0.95​Cs0.05_{0.05}0.05​PbI3_33​ lead halide perovskite crystal. Using periodic laser pulses, we synchronize the electron spin Larmor precession about an external magnetic field in an inhomogeneous ensemble, the effect known as spin mode locking. It appears as a decay of the optically created ensemble spin polarization within the dephasing time T2∗T_2^*T2∗​ of up to 20 ns and its revival during the spin coherence time T2T_2T2​ reaching the millisecond range. This exceptionally long spin coherence time in a bulk crystal is complemented by millisecond-long longitudinal spin relaxation times T1T_1T1​ for electrons and holes, measured by optically-detected magnetic resonance. These long-lasting spin dynamics highlight perovskites as promising platform for the quantum devices with all-optical control.
Millisecond spin relaxation times of distinct electron and hole subensembles in MAx_xx​FA1−x_{1-x}1−x​PbI3_33​ perovskite crystals
The unique combination of outstanding optical quality and attractive spin properties opens new avenues for optical spin control in hybrid organic-inorganic perovskite semiconductors. Using the optically detected magnetic resonance technique, we study the spins of electrons and holes in mixed-cation MAx_xx​FA1−x_{1-x}1−x​PbI3_33​ single crystals with x=0.4x = 0.4x=0.4 and 0.8. Multiple distinct spin subensembles with ggg-factors spanning from 2.9 to 3.6 for electrons and from 0.5 to 1.2 for holes are resolved, revealing diverse localization environments. We measure the longitudinal spin relaxation times, T1T_1T1​, reaching 2 ms and remaining in the μμμs range even for weakly localized carriers at the cryogenic temperature of 1.6 K. The magnetic-field dependence of T1T_1T1​ is dominated by the random nuclear (Overhauser) fields with strengths of ∼0.4−0.8\sim 0.4-0.8∼0.4−0.8 mT for electrons and ∼4−12\sim 4-12∼4−12 mT for holes, corresponding to μμμs-long correlation times of the hyperfine field determined by carrier hopping between shallow localization sites. The temperature dependence of T1T_1T1​ reveals a weak localization potential of the charge carriers and shows a correlation between T1T_1T1​ and the inhomogeneity of the spin ensemble. These results establish mixed-A-site perovskite single crystals as a promising solid-state platform with long-lived spin states for quantum information applications.
The coherent spin dynamics of resident carriers, electrons, and holes in semiconductor nanostructures is studied theoretically under the conditions of periodical optical excitation using short laser pulses and in an external magnetic field. The generation and dephasing of spin polarization in an ensemble of carrier spins, for which the relaxation time of individual spins exceeds the repetition period of the laser pulses, are analyzed. Accumulation of the spin polarization is manifested either as resonant spin amplification or as mode locking of carrier spin coherences. It is shown that both regimes have the same origin, while their appearance is determined by the optical pump power and the spread of spin precession frequencies in the ensemble.
Abstract Nanoscale systems that coherently couple to light and possess spins offer key capabilities for quantum technologies. However, an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. Here, we report optically controlled nuclear spins with long coherence lifetimes (T2) in rare-earth-doped nanoparticles. We detect spins echoes and measure a spin coherence lifetime of 2.9 ± 0.3 ms at 5 K under an external magnetic field of 9 mT, a T2 value comparable to those obtained in bulk rare-earth crystals. Moreover, we achieve spin T2 extension using all-optical spin dynamical decoupling and observe high fidelity between excitation and echo phases. Rare-earth-doped nanoparticles are thus the only nano-material in which optically controlled spins with millisecond coherence lifetimes have been reported. These results open the way to providing quantum light-atom-spin interfaces with long storage time within hybrid architectures.
We demonstrate an entirely new method to probe quantum measurement phenomena in semiconductor quantum dot (QD) spin qubits [1]. In addition to providing direct evidence for the quantum nature of solid state qubits, we show that our method has practical importance since it provides a completely alternative route for measuring ensemble and quantum dephasing times, T2* and T2, using only repeated projective measurements and without the need for coherent spin control. Our approach is based on measuring time-correlators of a spin qubit in an optically active QD beyond the second order. We utilize a quantum dot spin-storage structure to initialize a single electron spin in a quantum dot subject to a magnetic field applied in Voigt geometry through tunnel ionization and perform repeated projective measurements of the spin at times t1 and t2. This measurement is repeated, corresponding to ensemble averaging, and the resulting third-order time correlations reveals rich physics: For times t1 or t2 < T2* Larmor precession is observed which reveals the ensemble dephasing time T2*. Importantly, even though the time-correlators were obtained through averaging many measurements for times t1 and t2 > T2* oscillations are observed that decay with the dephasing time T2 and allow its determination even without the need for coherent spin control. Finally, combining the third-order time correlator with the second-order time correlator allows to demonstrate a violation of Leggett-Garg type inequalities for certain times providing clear evidence for the quantum nature of the quantum dot spin. [1] A. Bechtold et al. Phys. Rev. Lett. 117, 027402 (2016)
Erbium-doped solids are prime candidates for quantum memories in optical quantum networks given their telecom-compatible photon emission. An electron spin of erbium with millisecond coherence time is desirable for generating remote entanglement between adjacent quantum network nodes. Here we report GHz-range electron-spin transitions of 167Er3+{}^{167}{\mathrm{Er}}^{3+}167Er3+ in a yttrium oxide (Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​) matrix with coherence times that are consistently longer than a millisecond. By polarizing paramagnetic impurity spins we achieve a spin T2{T}_{2}T2​ up to 1.46 ms, and up to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the longest found for erbium in crystalline matrices despite the presence of host nuclear spins. We further enhance the coherence time beyond conventional dynamical decoupling, using customized sequences to simultaneously mitigate spectral diffusion and dipolar interactions. Our study not only establishes 167Er3+{}^{167}{\mathrm{Er}}^{3+}167Er3+: Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​ as a significant quantum memory platform but also provides a guideline for engineering long-lived erbium spins in a variety of host materials for quantum technologies.
The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study 3-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2T_ 2T2​ = 0.45 ns which is determined by the radiative lifetime of trions T1T_1T1​ = 0.27 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,eT_{2,e}T2,e​ ~ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.