Observation of collective excitation of two individual atoms in the Rydberg blockade regime

Abstract

The dipole blockade between Rydberg atoms has been proposed as a basic tool in quantum information processing with neutral atoms. Here we demonstrate experimentally the Rydberg blockade of two individual atoms separated by 4 µm. Moreover, we show that, in this regime, the single atom excitation is enhanced by a collective two-atom behavior associated with the excitation of an entangled state. This observation is a crucial step towards the deterministic manipulation of entanglement of two or more atoms using the Rydberg dipole interaction.PACS numbers: 32.80. Rm, 03.67.Lx, 32.80.Pj, 42.50.Ct A large experimental effort is nowadays devoted to the production of entanglement, that is quantum correlations, between individual quantum objects such as atoms, ions, superconducting circuits, spins, or photons. Entangled states are important in many areas of physics such as quantum information and quantum metrology, the study of strongly correlated systems in many-body physics, and more fundamentally in the understanding of quantum physics.There are several ways to engineer entanglement in a quantum system. Here, we focus on a method that relies on a blockade mechanism where the strong interaction between different parts of a system prevents their simultaneous excitation by the same driving pulse. Single excitation is still possible, but it is delocalized over the whole system, and results in the production of an entangled state. This approach to entanglement is deterministic and can be used to realize quantum gates [1] or to entangle mesoscopic ensembles, provided that the blockade is effective over the whole sample [2]. Blockade effects have been observed in systems where interactions are strong such as systems of electrons using the Coulomb force [3] or the Pauli effective interaction [4], as well as with photons and atoms coupled to an optical cavity [5]. Recently, atoms held in the ground state of the wells of an optical lattice have been shown to exhibit interaction blockade, due to s-wave collisions [6].An alternative approach uses the comparatively strong interaction between two atoms excited to Rydberg states, which have very large dipole moments. This strong interaction gives rise to the so-called Rydberg blockade, which has been observed in clouds of cold atoms [7,8,9,10,11,12] as well as in a Bose condensate [13]. A collective behavior associated with the blockade has been reported in an ultra-cold atomic cloud [14]. Recently, an experiment demonstrated the blockade between two atoms 10 µm apart, by showing that when one atom is excited to a Rydberg state, the excitation of the second one is greatly suppressed [15].In the present work, we study two individual atoms, held at a distance of ∼ 4 µm by two optical tweezers. We demonstrate that under this condition, the atoms are in the Rydberg blockade regime since only one atom can be excited. Furthermore, we show that the single atom excitation is enhanced by a collective two-atom behavior, associated with the production of a two-atom entangled state between th...

Radiative and collisional processes in translationally cold samples of hydrogen Rydberg atoms studied in an electrostatic trap

“…The properties of Rydberg states also depend on the orbital and magnetic quantum numbers and m. The selective production of Rydberg states of well-defined quantum numbers enables one to generate atoms or molecules with specific physical properties. This advantage is exploited in an increasing number of scientific applications in several subfields of physics and chemistry, such as quantum optics (see, e.g., [4,5]), quantum-information science (see, e.g., [6,7]), metrology in atoms and molecules (see, e.g., [8][9][10]), high-resolution photoelectron spectroscopy [11], the sensing of electromagnetic fields [12][13][14], and in research on antihydrogen [15][16][17].…”

Quantum nonlinear optics with single photons enabled by strongly interacting atoms

“…Here we demonstrate a medium that is nonlinear at the level of individual quanta, exhibiting strong absorption of photon pairs while remaining transparent to single photons. The quantum nonlinearity is obtained by coherently coupling slowly propagating photons [3][4][5] to strongly interacting atomic Rydberg states [6][7][8][9][10][11][12] in a cold, dense atomic gas 13 . Our approach opens the door for quantum-byquantum control of light fields, including single-photon switching 14 , all-optical deterministic 1 quantum logic 15 , and the realization of strongly correlated many-body states of light 16 .…”

“…EIT nonlinearities at the few-photon level have been previously observed without using strongly interacting atomic states by means of strong transverse confinement of the light 28,29 . The interactions between cold Rydberg atoms have been explored in ensembles [6][7][8][9][10] and have been used to realize quantum logic gates between two Rydberg atoms 11,12,24 . Giant optical nonlinearities using Rydberg EIT 14,22,23 have been observed in a classical, multi-photon regime 13 .…”

Single atoms in the ring lattice for quantum information processing and quantum simulation

“…Chin Sci Bull, 2012Bull, , 57: 1931 1945Bull, , doi: 10.1007 Single neutral atoms are promising candidates for quantum information processing [6,7]. A qubit can be encoded in the internal or motional states of an atom, and multi-qubit operations can be performed based on atom-light interactions or atom-atom interactions.…”

“…The preparation and manipulation of single atoms in optical microscopic potentials open a route to deterministically controlling the quantum states. Due to the good scalability and long coherence time, these quantum systems have been employed to demonstrate quantum gate [4] and entanglement of atoms [5] based on "Rydberg blockade" effect [6,7]. A qubit can be encoded in the internal or motional states of an atom, and multi-qubit operations can be performed based on atom-light interactions or atom-atom interactions.…”