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Journal of the Optical Society of America B

Ultrafast nuclear spin polarization for isotopes with large nuclear spin

Takashi Nakajima

Published Mar 3, 2009• 2 citations
Publisher

Abstract

We theoretically investigate the temporal dynamics of nuclear spin induced by short laser pulses. To realize ultrafast nuclear spin polarization, we coherently excite the hyperfine manifolds and let it evolve in time. An appropriate choice of the state with large hyperfine splittings allows us to realize ultrafast nuclear spin polarization. As specific examples, we consider the various isotopes of Mg and Ca with different values of nuclear spin (1/2, 3/2, 5/2, and 7/2) and show that 89%, 76%, 49%, and 36% of nuclear spin polarization can be achieved, respectively, within a few nanoseconds, which is at least 2 to 3 orders of magnitude shorter than the time needed for any known optical methods. Because of its ultrafast nature, our scheme would be very effective not only for stable nuclei but also unstable nuclei with a lifetime as short as 1 μs.

DOI
10.1364/josab.26.000572

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We theoretically investigate the temporal dynamics of nuclear spin induced by short laser pulses. To realize ultrafast nuclear spin polarization, we coherently excite the hyperfine manifolds and let it evolve in time. An appropriate choice of the state with large hyperfine splittings allows us to realize ultrafast nuclear spin polarization. As specific examples, we consider the various isotopes of Mg and Ca with different values of nuclear spin (1/2, 3/2, 5/2, and 7/2) and show that 89%, 76%, 49%, and 36% of nuclear spin polarization can be achieved, respectively, within a few nanoseconds, which is at least 2 to 3 orders of magnitude shorter than the time needed for any known optical methods. Because of its ultrafast nature, our scheme would be very effective not only for stable nuclei but also unstable nuclei with a lifetime as short as 1 μs.
We present a scheme to control the spin-polarization of photoelectrons/photoions using short laser pulses. It is based on the pump-probe method. By exciting fine structure manifolds of a system by the short pump pulse with a sufficient bandwidth, a superposition of fine structure states is created. After the pump pulse, the coherently superposed excited state evolves in time under the field-free condition with a period determined by the inverse of energy difference between them. In terms of the spin state, this suggests that the different spin state evolves differently in time, leading to the time-varying spin-polarization. Therefore, varying the time delay between the pump and probe pulses leads to the control of spin states upon photoionization. Specific theoretical results are presented for two-valence-electron atoms, in particular for Mg, which demonstrate that, under certain conditions, not only the degree of spin-polarization but also its polarity can be manipulated through time delay. Furthermore, we propose a new technique to accelerate the coupling time by the introduction of a dressing laser with a few ns duration. Since the underline physics is rather general and transparent, the presented scheme may be potentially applied to nanostructures such as quantum wells and quantum dots.
Nuclear polarization plays an essential role in precision measurements, symmetry tests, and emerging quantum technologies, yet efficient polarization of heavy nuclei remains a major challenge. We propose an efficient, intense-laser-based approach that achieves high-efficiency polarization of heavy nuclei through the nonlinear interaction of circularly polarized femtosecond laser pulses with hydrogenlike ions. This scheme enables rapid transfer of angular momentum from light to the nucleus. Numerical simulations show that a single pulse can generate polarization exceeding 10%, while a pulse sequence can drive the system to near-unity polarization. The method is broadly applicable to heavy ions with large hyperfine splittings, as demonstrated for ^{229}Th, ^{205}Pb, and ^{209}Bi. The ability to produce near-complete polarization of large-spin nuclei and heavy ions opens new avenues for nuclear physics and nucleus-based quantum technologies.
The nuclear spin in the vicinity of a nitrogen-vacancy (NV) center possesses long coherence time and convenient manipulation assisted by the strong hyperfine interaction with the NV center. It is suggested for the subsequent quantum information storage and processing after appropriate initialization. However, current experimental schemes are either sensitive to the inclination and magnitude of the magnetic field or require thousands of repetitions to achieve successful realization. Here, we propose a method to polarize a 13C^{13}\mathrm{C}13C nuclear spin in the vicinity of an NV center via a dark state. We demonstrate theoretically and numerically that it is robust to polarize various nuclear spins with different hyperfine couplings and noise strengths.
Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g., vanadium, emit in one of the telecom bands, but the large ground-state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long time coherent storage of quantum states. The proposed nuclear-spin preparation protocol thus marks the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.
Optical experiments in alkali-metal atomic gases are usually interpreted in terms of the J=1/2 ground state, treating the electronic ground state as a degenerate two-level system. While this simplified level scheme has been quite successful in describing many experimental results, the nuclear spin can lead to significant modifications of the behavior. Apart from the obvious differences, such as the existence of hyperfine splitting, some more subtle effects are present that modify the dynamical as well as the equilibrium behavior of the system. An an example, the optical pumping process in the true atomic ground state is nonexponential and slower by at least an order of magnitude, compared to a hypothetical atom with nuclear spin zero. The limitations of the J=1/2 model are analyzed theoretically and experimentally for atomic sodium, and experimental methods are demonstrated that can help disentangle the contributions from different hyperfine components.