Abstract
We investigate experimentally the effect of time dependent magnetic fields on the spin dynamics of the Carr - Purcell - Meiboom - Gill (CPMG) sequence. Over a wide range of offset fields and ramp rates, the measured response is fully consistent with adiabatic behavior. The echo amplitudes exhibit characteristic modulations that are in excellent agreement with theoretical predictions. Non-adiabatic events are observed at distinct offsets. Abruptly after passing through these offsets, the experimental results deviate from the theoretical adiabatic expressions. These non-adiabatic events occur precisely at the field offsets predicted by theory. It is demonstrated that in the adiabatic regime the effects of field fluctuations are fully reversible, while the occurrence of non-adiabatic events leads to hysteresis. The adiabatic range of field offsets can be increased by modifying the refocusing pulses within the CPMG sequence.
Highlights
When a quantum system is driven through multiple avoided energy-level crossings, the occurrence of nonadiabatic transitions in the vicinity of these crossings can lead to interesting quantum interference phenomena
We have applied and tested a framework to characterize the response of CPMG-like sequences to time-dependent magnetic fields
We have shown that the response can be generally classified into adiabatic behavior that is occasionally interrupted by nonadiabatic events
Summary
When a quantum system is driven through multiple avoided energy-level crossings, the occurrence of nonadiabatic transitions in the vicinity of these crossings can lead to interesting quantum interference phenomena. The resulting constructive or destructive quantum interference pattern, sensitive to the amplitude and frequency of the driving field and the gap between the two levels, has been used to demonstrate and simulate such quantum phenomena as the universal conductance fluctuation and the weak localization [2,3]. This interference effect associated with nonadiabatic transitions at the passage near avoided crossings has been observed mostly in effective two-level systems with Rydberg atoms [4] and superconducting qubits [5,6].
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