Experimental realization of a quantum ratchet through phase modulation

Abstract

We report on an experimental realization of unidirectional transporting island structures in an otherwise chaotic phase space of the δ-kicked rotor system. Using a Bose-Einstein condensate as a source of ultracold atoms, we employ asymmetric phase modulation in the kicks, with the narrow momentum distribution of the atoms allowing us to address individual island structures. We observe quantum ratchet behavior in this system, with clear directed momentum current in the absence of a directional force, which we characterize and connect to -classical theory.

Experimental realization of a momentum-space quantum walk

“…The quantum resonant ratchet effect requires breaking the spatial-temporal symmetry of the problem [44,45,57,58] to direct the dynamics of the AOKR in momentum space accordingly. Experimentally, this is achieved by the choice of an initial state 1/ √ 2(|n = 0 + e iφ |n = 1 ) created by a long pulse of the off-resonant standing wave (Bragg pulse) on the original BEC (|n = 0 ) [44,59].…”

Ratchet effect in the quantum kicked rotor and its destruction by dynamical localization

“…In the following, we will focus on relatively small values ofk, in the range 0.8-1.3, allowing us to study both the (semi-) classical dynamics and dynamical localization. A similar Hamiltonian displaying an interplay between a quantum resonance, observed fork = 2π , and accelerator modes has been studied experimentally [24,36,37]. In our case, in contrast, the ratchet effect is purely classical, and is therefore independent of the value ofk.…”

Phase noise in the delta kicked rotor: from quantum to classical

“…We begin with a 87 Rb BEC of approximately 20 000 atoms, prepared in an all-optical BEC machine [25]. The setup is similar to that of our previous phase modulated kicked rotor work [9].…”

“…In a similar vein, when the Overlay of quantum simulations, conducted through Floquet operations on an initial wavepacket, and calculations based on the Fourier spectrum in (7). (a) 7.5 kHz modulation with summation in (9) and (b) 15 kHz modulation with summation in (9). The energy has been scaled to a maximum value of 1.…”