Cooling to the Ground State of Axial Motion for One Atom Strongly Coupled to an Optical Cavity

Abstract

Localization to the ground state of axial motion is demonstrated for a single, trapped atom strongly coupled to the field of a high finesse optical resonator. The axial atomic motion is cooled by way of coherent Raman transitions on the red vibrational sideband. An efficient state detection scheme enabled by strong coupling in cavity QED is used to record the Raman spectrum, from which the state of atomic motion is inferred. We find that the lowest vibrational level of the axial potential with zero-point energy @! a =2k B 13 K is occupied with probability P 0 ' 0:95. DOI: 10.1103/PhysRevLett.97.083602 PACS numbers: 42.50.Pq, 03.67.ÿa, 32.80.Pj Single atoms strongly coupled to the fields of high quality optical resonators are of fundamental importance in quantum optics and, more generally, can be used for many tasks in quantum information science, including the implementation of scalable quantum computation [1,2] and the realization of distributed quantum networks [3,4]. In recent years, significant experimental progress to develop tools suitable for these tasks has been made by employing optical forces to localize individual atoms within optical cavities in a regime of strong coupling [5][6][7][8][9][10][11], as well as by combining trapped ions with optical cavities [12]. Scientific advances thereby enabled include the observation of the vacuum-Rabi spectrum for an individual atom [9] and vacuum-stimulated cooling [10].Although great strides are being made with atoms localized and strongly coupled to the fields of optical cavities, it has not previously been possible to access the quantum regime for the atomic center-of-mass motion in cavity QED. Qualitatively new phenomena have been predicted in this regime for which a quantized treatment is required for both the internal (i.e., the atomic dipole and cavity field) and external (i.e., atomic motion) degrees of freedom, as was first recognized in the seminal work of Refs. [13][14][15] and in the years since [16 -22]. Examples include the transfer of quantized states of atomic motion to quantum states of light, and conversely [22], as well as for measurements that surpass the standard quantum limit for sensing atomic position [16].Our effort towards quantum control of atomic motion in cavity QED follows the remarkable set of achievements for trapped ions [23] and atoms in optical lattices [24], for which such control has led to the creation of manifestly quantum states of motion and to the manipulation of quantum information. A first step in many of these investigations has been the capability to cool to the ground state of motion for single trapped atoms or ions.In this Letter, we report localization to the ground state of motion for one atom trapped in an optical cavity in a regime of strong coupling [11]. Resolved sideband cooling to the ground state is accomplished with a coherent pair of intracavity Raman fields. To deduce the resulting state of atomic motion, we introduce a scheme for recording Raman spectra by way of the interaction of the atom with a ...

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