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Physical Review Letters

Dynamics of Two Overlapping Spin Ensembles Interacting by Spin Exchange

Thomas W. Kornack, Michael V. Romalis

Published Dec 4, 2002• 230 citations
Publisher

Abstract

We describe linear and nonlinear dynamics of spin-polarized K and 3He ensembles interacting by spin exchange. The interactions are dominated by the imaginary part of the spin-exchange cross section and each spin species is primarily affected by the average magnetization of the other. Operating in a very low magnetic field we demonstrate novel dynamics when the electron and nuclear spin precession frequencies are nearly matched. We observe transverse damping as well as a dynamic instability of the 3He spins interacting with polarized K vapor. We also demonstrate operation as a self-compensating comagnetometer, useful for tests of CPT violation and other precision measurements.

DOI
10.1103/physrevlett.89.253002

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Interaction between spin polarized alkali atoms

Victor A. Kartoshkin

Collisions of alkali-metal atoms in the ground state with the electron spin S = 1/2 are accompanied by exchange of electron coordinates between colliding particles, which leads to polarization transfer between them (i.e., to the well-known phenomenon of spin exchange). In addition, along with the polarization transfer from one partner to another, the magnetic resonance lines of colliding atoms are broadened and shifted in spin-exchange collisions. In particular the last two processes depend on the complex spin-exchange cross section. The real part of the cross section determines the so-called "spin-exchange cross section," which is responsible for the broadening of magnetic resonance lines, while the imaginary part determines the shift cross section, which governs the frequency shift of magnetic resonance. In order to describe the spin-exchange process one have to know complex spin-exchange cross sections. Complex spin-exchange cross sections are calculated on the basis of the data on the singlet (X 1 Σ + ) and triplet (a 3 Σ + ) potentials describing the interaction alkali-metal atoms in the ground state. Collisions of alkali-metal atoms Cs, Rb, K, Na in the ground state are considered in the energy interval of 10 −4 −10 −2 au.

Journal of Physics Conference Series•Dec 1, 2018•0 citations
We describe linear and nonlinear dynamics of spin-polarized K and 3He ensembles interacting by spin exchange. The interactions are dominated by the imaginary part of the spin-exchange cross section and each spin species is primarily affected by the average magnetization of the other. Operating in a very low magnetic field we demonstrate novel dynamics when the electron and nuclear spin precession frequencies are nearly matched. We observe transverse damping as well as a dynamic instability of the 3He spins interacting with polarized K vapor. We also demonstrate operation as a self-compensating comagnetometer, useful for tests of CPT violation and other precision measurements.
Abstract We report on the dynamics of spin-polarized Rb and 21 Ne ensembles in which the 21 Ne spin ensemble in a glass vapor cell experiences a high magnetic field produced by a Rb electron-spin ensemble. The coupled spin ensembles are modeled and the response of the transverse-step magnetic field excitation is solved and studied experimentally. Moreover, we analyze the frequency response of the ensembles to a transverse-oscillating magnetic field. We demonstrate the strong transverse damping and large frequency shift of the 21 Ne spin ensemble as the precession frequencies of 21 Ne spin and Rb spin match and the magnetic resonance spectroscopies of the two ensembles merge into one. We also demonstrate the operation of the spin ensembles as a self-compensating co-magnetometer that is insensitive to low-frequency magnetic fields that would be useful for rotation rate sensing. For such sensing applications, a large Rb density is achieved to polarize the 21 Ne spins. This density leads to a high Rb electron spin magnetic field and we demonstrate its effect on the dynamics of the co-magnetometer.
Spin manipulation and detection of alkali-metal and noble-gas ensembles in spin-exchange-relaxation-free (SERF) comagnetometers are widely used in fundamental physical research, and have potential for inertial navigation. The dynamic behavior of spin ensembles is a vital characteristic that determines the applicability of comagnetometers, which significantly differs from various combinations of alkali-metal and noble-gas species. We comprehensively study the critical dynamics of strongly interacting ensembles in SERF comagnetometers with different species combinations. Different from the self-compensation point, a model of strong coupling point at which the dynamics is nonlinear because two ensembles influence each other strongly is established. We verify it by comparing the transient and steady-state dynamics of K-Rb-21Ne{}^{21}\mathrm{Ne}21Ne, K-Rb-3He{}^{3}\mathrm{He}3He, and K-3He{}^{3}\mathrm{He}3He comagnetometers with various input signals. The K-Rb-21Ne{}^{21}\mathrm{Ne}21Ne comagnetometer has a better potential for bandwidth and sensitivity in inertial measurement. Besides, we propose a critical point where the response rate of coupling spin ensembles is optimal among all polarization, and the critical dynamics is verified experimentally to be in agreement with theoretical simulations. The damping rate and precession frequency at the critical point can be more than 5 times larger than that at typical optimal spin polarization. Enhancement of spin-ensemble coupling strength improves the response rate of SERF comagnetometers and paves the way for efficient manipulation of noble-gas atoms via alkali-metal atoms in quantum information.
change interaction. In a K-Rb- 21 Ne co-magnetometer which was used for rotation sensing, Rb atomic spins and the 21 Ne nuclear spins couple together by spin exchange. Due to the large Rb density and the Fermi contact constant of Rb- 21 Ne pair, the magnetization field of Rb atomic spins is much larger than that of the K in a K- 3 He co-magnetometer. At the co-magnetometer working point, the precession frequency of Rb atomic spins are much larger than that of the 21 Ne spins. The decay rate and precession frequency of 21 Ne atoms is much smaller than that of the point when the precession frequencies of the Rb and 21 Ne atoms are the same. In this experiment, the dynamics of the Rb- 21 Ne pair at different holding magnetic field point were studied. The frequency response of the co-magnetometer to oscillating magnetic field at different holding magnetic field point was also studied.
We demonstrate a method for simultaneously measuring the spin polarizations of noble-gas and alkali-metal atoms. Under a low magnetic field, the polarized alkali-metal and noble-gas spin ensembles exhibit novel dynamics in the self-compensation and resonance regimes, which can be used to measure the polarizations. We perform this method on a K\mathrm{K}K-Rb\mathrm{Rb}Rb-21{}^{21}21Ne\mathrm{Ne}Ne comagnetometer with various operation temperatures and pump-light intensities. The polarization of alkali-metal electrons from 0.245 to 0.964 and the polarization of noble-gas nuclear spins from 0.01 to 0.065 are measured with relative uncertainties less than $12.4\mathrm{%}$. The measured polarizations are consistent with the theoretical model and are also verified by the traditional polarization-measurement method.
Highly polarized 3He ensembles prepared by metastability-exchange optical pumping (MEOP) have been widely used in precision measurements and fundamental physics. Metastability-exchange (ME) collisions, serving as the basis of MEOP, are traditionally described in terms of atomic orientation, while the significant contributions of metastable alignment tensor at high polarization remain unexplored. In this work, we develop a linearized model under mean-field approximation to investigate alignment tensor effects in highly polarized 3He , which originate from the metastable F = 3/2 manifold and are revealed through ME-induced relaxation and frequency shift. By means of free-induction-decay (FID) measurements, a pronounced dependence on nuclear polarization is experimentally observed in the response of the ground-state-metastable hybrid 3He ensembles to the external magnetic field. Furthermore, after obtaining the characteristics of tensor-induced phenomena, we demonstrate good agreement between the experiment and the theory. This work advances the understanding of nuclear spin dynamics in highly polarized 3He using MEOP. It further provides applications in systematic error correction of high-accuracy magnetometry, as well as in optimal protocol for the generation of nuclear spin-squeezed states.
Collisions of alkali-metal atoms in the ground state with the electron spin S = 1/2 are accompanied by exchange of electron coordinates between colliding particles, which leads to polarization transfer between them (i.e., to the well-known phenomenon of spin exchange). In addition, along with the polarization transfer from one partner to another, the magnetic resonance lines of colliding atoms are broadened and shifted in spin-exchange collisions. In particular the last two processes depend on the complex spin-exchange cross section. The real part of the cross section determines the so-called "spin-exchange cross section," which is responsible for the broadening of magnetic resonance lines, while the imaginary part determines the shift cross section, which governs the frequency shift of magnetic resonance. In order to describe the spin-exchange process one have to know complex spin-exchange cross sections. Complex spin-exchange cross sections are calculated on the basis of the data on the singlet (X 1 Σ + ) and triplet (a 3 Σ + ) potentials describing the interaction alkali-metal atoms in the ground state. Collisions of alkali-metal atoms Cs, Rb, K, Na in the ground state are considered in the energy interval of 10 −4 −10 −2 au.