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Il Nuovo cimento della Società italiana di fisica. B/Il Nuovo cimento B

Classical and quantum «EPR»-spin correlations in the triplet state

A. O. Barut, M. Bozič

Published May 1, 1988• 4 citations
Publisher
DOI
10.1007/bf02748963

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Abstract The photoexcited triplet state of fullerene is a promising system for molecular qutrits, as it exhibits long coherence times, well‐defined multilevel quantum states in transient electron paramagnetic resonance (EPR) processes, and the advantage of easy initialization following laser radiation. However, in pristine C60, the frequency range of the EPR signal often exceeds the bandwidth of the EPR pulses due to the large zero‐field splitting effect of the localized S = 1 spin centers. This significantly hinders the selective excitation of signals at optimal positions and limits the precise quantum gating of the transient spins. To address this challenge, C60 has been modified with palladium porphyrin (PdP), forming a donor‐acceptor complex that enhances the delocalization of the triplet state's electronic spin. This modification significantly narrows the peak spacing of the triplet EPR spectrum. The quantum coherence properties of PdP‐C60 are characterized and successfully prepared a clear three‐level superposition state. Furthermore, quantum phase interference experiments validated the system's controllability as a molecular qutrit, which can achieve coherent multi‐level superposition states. This work provides new insights and methods for exploiting fullerene derivatives in quantum control and information processing applications.
There is an opinion that the Bohm reformulation of the EPR paradox in terms of spin variables is equivalent to the original one. In this note we show that such an opinion is not justified. We apply to the original EPR problem the method which was used by Bell for the Bohm reformulation. He has shown that correlation function of two spins cannot be represented by classical correlation of separated bounded random processes. This Bell`s theorem has been interpreted as incompatibility of local realism with quantum mechanics. We show that, in contrast to Bell`s theorem for spin or polarization correlation functions, the correlation of positions (or momenta) of two particles, depending on the rotation angles, in the original EPR model always admits a representation in the form of classical correlation of separated random processes. In this sense there exists a local realistic representation for the original EPR model but there is no such a representation for the Bohm spin reformulation of the EPR paradox. It shows also that the phenomena of quantum nonlocality is based not only on the properties of entangled states but also on the using of particular bounded observables.