Abstract
A quantum system interacting with its environment is subject to dephasing, which ultimately destroys the information it holds. Here we use a superconducting qubit to experimentally show that this dephasing has both dynamic and geometric origins. It is found that geometric dephasing, which is present even in the adiabatic limit and when no geometric phase is acquired, can either reduce or restore coherence depending on the orientation of the path the qubit traces out in its projective Hilbert space. It accompanies the evolution of any system in Hilbert space subjected to noise.
Highlights
A quantum system interacting with its environment is subject to dephasing, which destroys the information it holds
Part of this dephasing is of geometric origin[2] and is related to a type of geometric phase known as Berry phase[3,4], which is accumulated when a quantum system is adiabatically steered along a closed contour in the parameter space of its Hamiltonian
The geometric phase roots in the structure of Hilbert space and is—unlike the dynamic phase—not related to the duration of a quantum process. When it comes to quantum dissipative systems, ubiquitous in our physical world, the nature of the geometric phase may be put to question: noise may screen out geometric effects and the condition for adiabaticity is not self-evident
Summary
A quantum system interacting with its environment is subject to dephasing, which destroys the information it holds. Decoherence in quantum systems stems from the stochastic evolution of the dynamic phase of the system’s wave function (dynamic dephasing), and from geometric effects. From equation (3), it follows that in a Ramsey experiment, in which the effective magnetic field performs n oriented loops in the time interval [0, T], the eigenstates of the qubit acquire a total relative phase g([0, T], n), where
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