Observation of coherent many-body Rabi oscillations

Abstract

A two-level quantum system coherently driven by a resonant electromagnetic field oscillates sinusoidally between the two levels at frequency $\Omega$ which is proportional to the field amplitude [1]. This phenomenon, known as the Rabi oscillation, has been at the heart of atomic, molecular and optical physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi oscillations in isolated single atoms or dilute gases form the basis for metrological applications such as atomic clocks and precision measurements of physical constants [3]. Both inhomogeneous distribution of coupling strength to the field and interactions between individual atoms reduce the visibility of the oscillation and may even suppress it completely. A remarkable transformation takes place in the limit where only a single excitation can be present in the sample due to either initial conditions or atomic interactions: there arises a collective, many-body Rabi oscillation at a frequency $N^0.5\Omega$ involving all N >> 1 atoms in the sample [4]. This is true even for inhomogeneous atom-field coupling distributions, where single-atom Rabi oscillations may be invisible. When one of the two levels is a strongly interacting Rydberg level, many-body Rabi oscillations emerge as a consequence of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to quantum information processing based on this effect [5]. Here we report initial observations of coherent many-body Rabi oscillations between the ground level and a Rydberg level using several hundred cold rubidium atoms. The strongly pronounced oscillations indicate a nearly complete excitation blockade of the entire mesoscopic ensemble by a single excited atom. The results pave the way towards quantum computation and simulation using ensembles of atoms

Effects of molecular resonances on Rydberg blockade

“…The outermost crossing with the most substantial laser coupling is at R × ≈ 6.2 μm. Since this value is larger than the average interatomic separation for typical experimental number densities [10] ρ d ≈ 10 11 −10 12 cm −3 , one may find a fraction of atomic pairs inside the volume-enclosing molecular resonance region.…”

“…This mechanism enables performing quantum logic operations between atom pairs and manipulate collective many-body states of an Natom ensemble [1]. Such collective states efficiently couple to laser fields with the coupling enhanced by a factor of √ N ; see experiments [10,11]. While a number of advanced protocols involving Rydberg blockade are being explored, an outstanding challenge is to identify and realize conditions for high-fidelity atomic and optical state control via Rydberg blockade.…”

Grover search algorithm with Rydberg-blockaded atoms: quantum Monte Carlo simulations

“…The interactioninduced level shifts suppress resonant optical excitation of Rydberg states of more than one atom within a certain blockade distance from each other [1,2]. This blockade effect can then be used to implement quantum logic gate operations between closely spaced atoms [3][4][5][6][7][8], or to realize atomic ensemble qubits with Rydberg superatoms which can accommodate at most one collective Rydberg excitation at a time [9][10][11][12][13].…”

Inelastic Multiple Scattering of Interacting Bosons in Weak Random Potentials

“…A consequence of the large polarizability is the effective energy level shift of atoms in the neighborhood of a Rydberg atom leading to a vanishing probability to be excited (if the laser is tuned with respect to the energy levels of a single Rydberg atom). Within this so-called exclusion or blockade volume with radius b only a single excitation is present [200] and can thus be shared among all N atoms leading e. g. to collective Rabi oscillations with enhanced frequency √ NΩ [201]. An explicit expression for the blockade radius is obtained by determining the interaction energy of two Rydberg atoms at a distance b and setting this equal to the collective laser coupling √ NΩ for the N atoms inside the blockade radius, leading to b = [C 6 /(Ω 1/ )] 2/13 [202], with being the average spacing between the atoms.…”