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Register a new userObservation of Time-domain Rabi Oscillations in the Landau-Zener Regime with a Single Electronic Spin
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Under resonant conditions, a long sequence of landau-zener transitions can lead to Rabi oscillations. Using a nitrogen-vacancy (NV) center spin in diamond, we investigated the interference between more than 100 Landau-Zener processes. We observed the new type of Rabi oscillations of the electron spin resulting from the interference between successive Landau-Zener processes in various regimes, including both slow and fast passages. The combination of the control techniques and the favorable coherent properties of NV centers provides an excellent experimental platform to study a variety of quantum dynamical phenomena.
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We study the dynamic behaviour of a quantum two-level system with periodically varying parameters by solving the master equation for the density matrix. Two limiting cases are considered: multiphoton Rabi oscillations and Landau-Zener transitions. The approach is applied to the description of the dynamics of superconducting qubits. In particular, the case of the interferometer-type charge qubit with periodically varying parameters (gate voltage or magnetic flux) is investigated. The time-averaged energy level populations are calculated as funtions of the qubits control parameters.
Two aspects of the classic two-level Landau--Zener (LZ) problem are considered. First, we address the LZ problem when one or both levels decay, i.e., $veps_j(t) to veps_j(t)-i Gamma_j/2$. We find that if the system evolves from an initial time $-T$ to a final time $+T$ such that $|veps_1(pm T)-veps_2(pm T)|$ is not too large, the LZ survival probability of a state $| j ra$ can {em increase} with increasing decay rate of the other state $|i e j ra$. This surprising result occurs because the decay results in crossing of the two eigenvalues of the instantaneous non-Hermitian Hamiltonian. On the other hand, if $|veps_1(pm T)-veps_2(pm T)| to infty$ as $T to infty$, the probability is {em independent} of the decay rate. These results are based on analytic solutions of the time-dependent Schrodinger equations for two cases: (a) the energy levels depend linearly on time, and (b) the energy levels are bounded and of the form $veps_{1,2}(t) = pm veps tanh (t/{cal T})$. Second, we study LZ transitions affected by dephasing by formulating the Landau--Zener problem with noise in terms of a Schr{o}dinger-Langevin stochastic coupled set of differential equations. The LZ survival probability then becomes a random variable whose probability distribution is shown to behave very differently for long and short dephasing times. We also discuss the combined effects of decay and dephasing on the LZ probability.
A two-level system traversing a level anticrossing has a small probability to make a so-called Landau-Zener (LZ) transition between its energy bands, in deviation from simple adiabatic evolution. This effect takes on renewed relevance due to the observation of quantum coherence in superconducting qubits (macroscopic Schrodinger cat devices). We report an observation of LZ transitions in an Al three-junction qubit coupled to a Nb resonant tank circuit.
Nonlinear effects in mesoscopic devices can have both quantum and classical origins. We show that a three-Josephson-junction (3JJ) flux qubit in the _classical_ regime can produce low-frequency oscillations in the presence of an external field in resonance with the (high-frequency) harmonic mode of the system, $omega$. Like in the case of_quantum_ Rabi oscillations, the frequency of these pseudo-Rabi oscillations is much smaller than $omega$ and scales approximately linearly with the amplitude of the external field. This classical effect can be reliably distinguished from its quantum counterpart because it can be produced by the external perturbation not only at the resonance frequency $omega$ and its subharmonics ($omega/n$), but also at its overtones, $nomega$.
We analyze the strong-coupling dynamics of a driven harmonic oscillator whose energy is modulated by a continuum of other bosonic modes. This type of system-bath interaction appears, for example, in optomechanical or equivalent circuit QED setups, where the frequency of a confined photonic mode depends linearly on a fluctuating boundary. Compared to the canonical spin-boson model, where coupling to bath modes only leads to decoherence, the role of the environment in such systems is more complex, since it also provides the only source of nonlinearity. We show that even for an unstructured bath, these environment-induced nonlinearities can dominate over decoherence processes resulting in Rabi oscillations and the formation of highly non-classical states. These findings provide important insights into the non-Markovian dynamics of higher-dimensional open quantum systems and for realizing few-photon optical nonlinearities through strong interactions with a bath.
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