Off-diagonal Geometric Phase of Two-Qubit System

Xiufeng Li, Mao-Fa Fang

X. X. Yi, Junli Chang

The effect of the intersubsystem coupling on the off-diagonal geometric phase in a composite system is investigated. We analyze the case where the system undergoes an adiabatic evolution. Two coupled qubits driven by time-dependent external magnetic fields are presented as an example; the off-diagonal geometric phase as well as the adiabatic condition are examined and discussed.

Arno Böhm, Ali Mostafazadeh, Hiroyasu Koizumi +2 more

Stefan Filipp, Erik Sjöqvist

We extend the off-diagonal geometric phase [Phys. Rev. Lett. 85, 3067 (2000)]] to mixed quantal states. The nodal structure of this phase in the qubit (two-level) case is compared with that of the diagonal mixed state geometric phase [Phys. Rev. Lett. 85, 2845 (2000)]]. Extension to higher dimensional Hilbert spaces is delineated. A physical scenario for the off-diagonal mixed state geometric phase in polarization-entangled two-photon interferometry is proposed.

Lech Jakóbczyk, M. Siennicki

Yuji Hasegawa, Rudolf Loidl, G. Badurek +4 more

Off-diagonal geometric phases acquired in the evolution of a spin-1/2 system have been investigated by means of a polarized neutron interferometer. Final counts with and without polarization analysis enable us to observe simultaneously the off-diagonal and diagonal geometric phases in two detectors. We have quantitatively measured the off-diagonal geometric phase for noncyclic evolutions, confirming the theoretical predictions. We discuss the significance of our experiment in terms of geometric phases (both diagonal and off- diagonal) and in terms of the quantum-erasing phenomenon.