Tunable open-access microcavities for on-chip cavity quantum electrodynamics

Abstract

We report on the development of on-chip microcavities and show their potential as a platform for cavity quantum electrodynamics experiments. Microcavity arrays were formed by the controlled buckling of SiO2/Ta2O5 Bragg mirrors, and exhibit a reflectance-limited finesse of 3500 and mode volumes as small as 35λ3 . We show that the cavity resonance can be thermally tuned into alignment with the D2 transition of 87 Rb, and outline two methods for providing atom access to the cavity. Owing to their small mode volume and high finesse, these cavities exhibit single-atom cooperativities as high as C1 = 65. A unique feature of the buckled-dome architecture is that the strong-coupling parameter g0/κ is nearly independent of the cavity size. Furthermore, strong coupling should be achievable with only modest improvements in mirror reflectance, suggesting that these monolithic devices could provide a robust and scalable solution to the engineering of light-matter interfaces.The implementation of a distributed quantum network could enable a global quantum communication system, [1,2] operations, [7,28] and to implement an elementary quantum network.[29] These works place single-atom quantum systems as a leading candidate for use in large-scale quantum networks. As a result, there is a strong interest in the integration of alkali atoms into robust, scalable, packaged optical cavities. [30,31] Furthermore, it is desirable for these optical cavities to have small mode volumes and be tunable to atomic transitions. [32][33][34] Here we report the development of 'buckled-dome' Fabry-Pérot microcavities designed for cQED applications, specifically on-chip coupling between single photons and single rubidium atoms. These cavities produce high single-atom cooperativities, can be easily tuned to atomic transitions, and can facilitate open-access for incorporation of atoms.The buckled-dome microcavities were fabricated via a monolithic self-assembly procedure. [35,36] First, a distributed Bragg reflector (10.5 periods SiO 2 /Ta 2 O 5 , starting and ending with Ta 2 O 5 ) was deposited on a fused silica substrate by reactive magnetron sputtering. Microcavities were defined by the lithographic patterning of a thin (∼15 nm) low-adhesion fluorocarbon layer, followed by the deposition of a second Bragg reflector identical to the initial reflector. Films with low loss and high compressive stress (∼200 MPa) were realized by using high target power (200 W), elevated substrate temperature (150• C), and low chamber pressure (4 mTorr).[37] Optical constants for single films were measured usarXiv:1601.03344v1 [cond-mat.mes-hall]

On-chip High-finesse Fabry-Perot Microcavities for Optical Sensing and Quantum Information

“…However, there are few options that promise fully monolithic integration of tunable high-finesse, open access microcavities on chips. Our group has reported a thin-film buckling approach [15,16,20,86] with potential to address this latter point. We've shown that circular delamination buckles can be controllably formed within a multilayer thin film stack, and that these features can behave as half-symmetric Fabry-Perot cavities.…”

“…However, fiber-based FPCs must be aligned with great precision, and misalignment errors combined with the lack of control over the divergence angle of the output beams can lead to low Q-factor [35,32,36,37]. In addition, fiber-based FPCs cannot be easily integrated onto (16) microfluidic chips; several post-fabrication steps are typically required to make them fully compatible for lab-on-a-chip applications. Nevertheless, only a few examples of fully monolithic integrated FPCs for optofluidic RI sensing exist, as briefly reviewed below.…”

“…The buckling self-assembly produces cavities with a high degree of geometrical perfection, characterized by cylindrically symmetric Laguerre-Gaussian modes and reflectance-limited finesse. Recently, Potts et al reported arrays of these microcavities [16] with SiO2/Ta2O5 Bragg mirrors, and exhibiting F ~ 3500 and mode volume ~ 35λ 3 . These cavities were designed for operation near 780 nm wavelength, and could be thermally tuned to the D2 transition of Rb.…”

“…In the following, we briefly summarize micro-machining approaches that have been used to fabricate hybrid-integrated cavities, with some emphasis on recent efforts aimed at the eventual monolithic integration of mirrors and cavities with other functional devices. [73], (b) a laser machined fiber end [12], (c) array of concave features made by FIB milling [11], (d) two silicon micro-mirrors fabricated by dry etching [74], (e) array of cantilever based micro-mirrors [75], (f) and a waveguide connected buckled-dome microcavity [16].…”

“…Others have employed wafer-bonding approaches combined with precision alignment stages [14]. However, the realization of truly monolithic, curved mirror FPCs with high F and low Vm remains at a relatively nascent stage of development [15,16].…”