3D Larmor clock and barrier interaction times for tunneling

D. Demir

J.I. Ramos, Shreyas Potnis, David Spierings +2 more

Fumika Suzuki, William George Unruh

We numerically study two methods of measuring tunneling times using a quantum clock. In the conventional method using the Larmor clock, we show that the Larmor tunneling time can be shorter for higher tunneling barriers. In the second method, we study the probability of a spin-flip of a particle when it is transmitted through a potential barrier including a spatially rotating field interacting with its spin. According to the adiabatic theorem, the probability depends on the velocity of the particle inside the barrier. It is numerically observed that the probability increases for higher barriers, which is consistent with the result obtained by the Larmor clock. By comparing outcomes for different initial spin states, we suggest that one of the main causes of the apparent decrease in the tunneling time can be the filtering effect occurring at the end of the barrier.

Jacek Jakiel

David Spierings, Aephraim M. Steinberg

How much time does a tunneling particle spend in a barrier? A Larmor clock, one proposal to answer this question, measures the interaction between the particle and the barrier region using an auxiliary degree of freedom of the particle to clock the dwell time inside the barrier. We report on precise Larmor time measurements of ultracold ^{87}Rb atoms tunneling through an optical barrier, which confirm longstanding predictions of tunneling times. We observe that atoms generally spend less time tunneling through higher barriers and that this time decreases for lower energy particles. For the lowest measured incident energy, at least 90% of transmitted atoms tunneled through the barrier, spending an average of 0.59±0.02 ms inside. This is 0.11±0.03 ms faster than atoms traversing the same barrier with energy close to the barrier's peak and 0.21±0.03 ms faster than when the atoms traverse a barrier with 23% less energy.

Miriam Deutsch, J. E. Golub

We exploit analogies between tunneling electrons and evanescent electromagnetic waves to construct and operate an optical Larmor clock. In the electronic Larmor clock, the tunneling time is proportional to the amount of precession the electronic spin undergoes while interacting with a weak, barrier-confined magnetic field. In the optical scheme, the analogy to the spin is made via Stokes parameters, and an optical retarder is shown to be analogous to the magnetic field. A magnetized tunnel barrier consists of a thin film of uniaxial liquid crystal between two high-index prisms. To operate the clock, we measure the Stokes parameters of the polarized laser beam transmitted through the barrier. By varying the wavelength of the incident light, we use the clock to study tunneling through barriers of various thicknesses. \textcopyright{} 1996 The American Physical Society.