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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Entangled electron spin states at work in spin dependent molecular processes

К. М. Салихов

Published Jun 1, 2005• 5 citations
Publisher

Abstract

There are summarized our results obtained when studying the entangled electron-hole pairs by the direct and indirect electron paramagnetic resonance methods. These results demonstrate rather peculiar response of the spins in the entangled state to the manipulations with the external microwave fields: intensities of lines in the electron paramagnetic resonance spectra should oscillate; the echo type signal is expected as the response to only one microwave pulse; the primary spin echo signal has anomalous phase compared to the phase of the echo signal in a case of spins in a non-entangled state; the two-quantum transitions can be manifested even in the absence of the spin-spin interaction if the electron paramagnetic resonance is detected indirectly, e.g., optically. A possible scenario for the quantum teleportation experiment is suggested.

DOI
10.1117/12.620305

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There are summarized our results obtained when studying the entangled electron-hole pairs by the direct and indirect electron paramagnetic resonance methods. These results demonstrate rather peculiar response of the spins in the entangled state to the manipulations with the external microwave fields: intensities of lines in the electron paramagnetic resonance spectra should oscillate; the echo type signal is expected as the response to only one microwave pulse; the primary spin echo signal has anomalous phase compared to the phase of the echo signal in a case of spins in a non-entangled state; the two-quantum transitions can be manifested even in the absence of the spin-spin interaction if the electron paramagnetic resonance is detected indirectly, e.g., optically. A possible scenario for the quantum teleportation experiment is suggested.
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Abstract One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. The “ghost” interference and the “ghost” image experiments demonstrated the astonishing nonlocal behavior of an entangled photon pair. Even though we still have questions in regard to fundamental issues of the entangled quantum systems, quantum entanglement has started to play important roles in quantum information and quantum computation. Quantum teleportation is one of the hot topics. We have demonstrated a quantum teleportation experiment recently. The experimental results proved the working principle of irreversibly teleporting an unknown arbitrary quantum state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that the complete set of Bell states can be distinguished in the Bell state measurement. Teleportation of a quantum state can thus occur with certainty in principle.
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Raman-heterodyne-detected paramagnetic resonance has been used to study the level anticrossing in the 3^{3}3A state of the N-V defect in diamond. The electron-paramagnetic-resonance (EPR) frequencies are well accounted for by a triplet-spin Hamiltonian. Comparison of the EPR spectra with the calculated transition dipole strengths indicates that optical pumping determines, to a large extent, the Raman-heterodyne-signal intensity. Spin alignment in the 3^{3}3A ground state under optical pumping leads to the collapse of the EPR signal at the level anticrossing, where the population is equalized due to the mixing of the spin states. This is substantiated by transient nutation and spin-echo measurements, from which the dipole moment and dephasing time are examined. Laser detuning within the 638-nm zero-phonon line shows that the Raman signal is only detectable when the laser frequency is tuned to the low-energy part of the optical line.
This thesis describes the Raman heterodyne detection of magnetic resonance in the ³A ground state of the nitrogen-vacancy C'-1· V) centre in diamond. The recently developed theory of Raman heterodyne spectroscopy was tested and compared with the spectra measured on the N-V centre. Among those results, the electron-nuclear double resonance (ENDOR), nuclear-nuclear double resonance (double NMR), Autler-Townes effect, coherence transfer and Zeeman quantum beat were observed for the first time using such techniques. Raman heterodyne techniques were also used to investigate the level anticrossing, hyperfine and nuclear quadrupole interactions, and spin relaxations of the N-V centre with high sensitivity and precision. This thesis is comprised of three parts. Part one includes Chapters 1 to 3, providing introductory accounts. Chapter l is an introduction to the N-V colour centre, which describes the defect configuration, the spin Hamiltonian and the calculations of energy levels and wave functions of the ³A ground state. Chapter 2 briefly describes the theory of Raman heterodyne spectroscopy - a coherent optical radio-frequency (RF) double resonance technique, in particular the Raman heterodyne signals at weak and intense RF fields. Chapter 3 deals with experimental details and techniques utilized in the studies. Part two consists of Chapters 4 and 5, where the Raman heterodyne theory is compared with experimental results. Chapter 4 presents the Raman heterodyne detected nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) lineshapes compared with theoretical results at various RF power levels, laser intensities and laser frequencies within the 6380A zero-phonon line. The double resonance spectra obtained by Raman heterodyne techniques are discussed in Chapter 5, where attention is paid to the analysis of their spectral profiles depending on the detection scheme. The application of Raman heterodyne techniques to the studies of magnetic resonance of the N-V centre is described in part three, consisting of Chapters 6 to 9. The EPR measurements are described in Chapter 6, which were used to study various interactions near the level anticrossing, in particular the spin alignment. The hyperfine and nuclear quadrupole interactions probed by the NMR, ENDOR and hole burning measurements are described in Chapter 7. From these measurements, the hyperfine and quadrupole parameters in the spin Hamiltonian were fully determined. Chapter 8 deals with the Autler-Townes effect in the NMR and EPR transitions. By measuring the Autler-Townes spittings, the magnitudes of matrix elements of the NMR transitions were examined and compared. Chapter 9 presents the coherent spin transient properties, including nutations, echoes, Zeeman beating and coherence transfer. The dephasing time and homogeneous linewidths of the NMR and EPR transitions were then determined from the echo measurements. Finally, the thesis is summarized in Chapter 10.