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arXiv:quant-ph/0602201

Density Matrix Tomography of Entangled Electron and Nuclear Spin States in 15N:C60

W. Scherer, Mehring, Michael

Published Feb 24, 2006• 0 citations
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Abstract

We discuss details of the preparation and detection of entangled electron-nuclear spin states in 15N:C60 together with a quantitative evaluation of the complete density matrix. All four Bell states of a two qubit subsystem were analyzed. In addition we find a quantum critical temperature of Tq = 7.73 K for this system at an electron spin resonance frequency of 95 GHz.

DOI
10.48550/arxiv.quant-ph/0602201

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We discuss details of the preparation and detection of entangled electron-nuclear spin states in 15N:C60 together with a quantitative evaluation of the complete density matrix. All four Bell states of a two qubit subsystem were analyzed. In addition we find a quantum critical temperature of Tq = 7.73 K for this system at an electron spin resonance frequency of 95 GHz.
Procedures of the preparation and detection of entangled electron-nuclear spin states in (15)N@C(60) by combining electron spin resonance and electron nuclear double resonance pulse techniques are presented. A quantitative evaluation of the complete density matrix is obtained by a special density matrix tomography. All four Bell states of a two qubit subsystem were analyzed and experimental decoherence times are presented. In addition, we estimate a quantum critical temperature of T(q)=7.76 K for this system at an electron spin resonance frequency of 95 GHz.
We have prepared combined electron and nuclear spin pseudoentangled states ${\ensuremath{\Psi}}_{27}^{\ifmmode\pm\else\textpm\fi{}}$ and ${\ensuremath{\Phi}}_{18}^{\ifmmode\pm\else\textpm\fi{}}$ out of the total number of eight quantum states in the multilevel quantum system of a nitrogen atom with electron spin 3/23/23/2 and nuclear spin 1/21/21/2 encaged in the endohedral fullerene 15N@C60^{15}\mathrm{N}@{\mathrm{C}}_{60}15N@C60​. Density matrix tomography was applied to verify the degree of entanglement.
Abstract This contribution concerns quantum information aspects in fullerenes. In particular we present here the preparation of pseudo‐pure states and pseudo‐entanglement in the coupled electron‐nucleus system P@C60 (S = 3/2 and I = 1/2) encapsulated in a solid state matrix. In this system the degeneracy of the high electron spin is lifted, allowing transition selective excitation. Density matrix tomography and phase rotations are applied for detecting pure states and entanglement The fidelity of the entangled state was determined to F = 0.93. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum computation depends on quantum entanglement, a correlation between subsystems that cannot occur classically. A variety of theoretical measures exist for quantifying the degree entanglement in such schemes, all of which are functions of the system density matrix. How can the entanglement be measured experimentally? Using quantum tomography techniques developed for two photon entangled states, the density matrix can be reconstructed from the appropriate experimental data. In this case the state tomography gives the complete characterization of the physical system (for the relevant degree of freedom, such as spin or polarization). It gives information on both the degree of nonclassical correlation, that is entanglement, as well as the amount of decoherence in the system. In this proceedings we discuss the general state tomography procedure required to characterize a few qubit quantum computer, for any architecture.