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Physical Review Letters

Coherence in freely precessing Ne21 and a test of linearity of quantum mechanics

T. E. Chupp, Rohan J. Hoare

Published May 7, 1990• 74 citations
Publisher

Abstract

We have observed coherence among the four magnetic sublevels of freely precessing $^{21}\mathrm{Ne}$ for times of 4.5 h. This has allowed direct detection of the quadrupole component of coherence relaxation and a test of linearity of quantum mechanics. The quadrupole component of relxation is evident in the different relaxation rates for the three lines of the NMR spectrum. Nonlinear corrections to quantum mechanics are found to be less than 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}26}$ of the binding energy per nucleon of $^{21}\mathrm{Ne}$.

DOI
10.1103/physrevlett.64.2261

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We have observed coherence among the four magnetic sublevels of freely precessing 21Ne^{21}\mathrm{Ne}21Ne for times of 4.5 h. This has allowed direct detection of the quadrupole component of coherence relaxation and a test of linearity of quantum mechanics. The quadrupole component of relxation is evident in the different relaxation rates for the three lines of the NMR spectrum. Nonlinear corrections to quantum mechanics are found to be less than 1.6\ifmmode\times\else\texttimes\fi{}10\ensuremath−26{10}^{\mathrm{\ensuremath{-}}26}10\ensuremath−26 of the binding energy per nucleon of 21Ne^{21}\mathrm{Ne}21Ne.
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The ability to live in coherent superpositions is a signature trait of quantum systems and constitutes an irreplaceable resource for quantum-enhanced technologies. However, decoherence effects usually destroy quantum superpositions. It was recently predicted that, in a composite quantum system exposed to dephasing noise, quantum coherence in a transversal reference basis can stay protected for an indefinite time. This can occur for a class of quantum states independently of the measure used to quantify coherence, and it requires no control on the system during the dynamics. Here, such an invariant coherence phenomenon is observed experimentally in two different setups based on nuclear magnetic resonance at room temperature, realizing an effective quantum simulator of two- and four-qubit spin systems. Our study further reveals a novel interplay between coherence and various forms of correlations, and it highlights the natural resilience of quantum effects in complex systems.
T. Blasberg: Coherent Raman scattering for optical detecti¬ on of NMR in Pr3+:YA103. Nuclear magnetic resonance (NMR) is a powerful and versatile spec¬ troscopic technique. However, conventional NMR requires samples, which has to consist of at least 1017 nuclear spins. One of the most promising approaches to increase the sensitivity of this method relies on the resonant interaction of laser fields with atoms. The main goal of this thesis was the investigation and the improvement of coherent Raman scattering techniques for an optical heterodyne detection of NMR. All ex¬ periments were performed at cryogenic temperatures on Pr3+-ions, which were added to the host lattice YAIO3 (YAP). The coherent Raman scattering experiments consist of two distinct stages: firstly, the transient or continuous excitation of a coherent superposition between two nuclear spin states and secondly, its optical detection through coherent Raman scattering of a resonant, frequency-tunable test laser field from this sublevel coherence. For the theoretical description of the experiments, coherent Raman scattering in multilevel atoms is discussed in detail and a common solution for the Raman heterodyne beat signal in pump-and-probe experiments is derived. The dynamics of a three-level atom that interacts with two resonant electromagnetic fields is treated making use of the density-matrix formalism. The method of Raman heterodyne detection of NMR uses a resonant radio frequency field to drive the magnetic-dipole transition between two nuclear spin states. 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Pr:YAP is therefore an ideal model system for the investigation of coherent Raman scattering. A new rf-optical triple-resonance experiment was developed that is a combination of Raman heterodyne detection of NMR and spectral holeburning. This technique allows the unambiguous determination of the ab¬ solute sign of nuclear quadrupole coupling constants. In the electronic ground state of PnYAP, the quadrupole coupling constant was found to be negative (D=-3.5289 MHz) being the result of dominant pseudoquadrupole contributions. The pump-and-probe technique, which uses a frequency-tunable test laser beam, was used to investigate the influence of an inhomogeneous broadening of the optical resonance line on Raman heterodyne detection of NMR. A hitherto unknown interference effect could be predicted and verified by the experiments. 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A simple rate-equation model allowed to calculate the entire hole-bur¬ ning spectrum of the crystal.