An array of integrated atom–photon junctions

Abstract

[1,2] efficient. In this letter we present the first waveguide chip designed to address a BEC along a row of independent junctions, which are separated by only 10 µm and have large atom-photon coupling. We describe the fully integrated, scalable design and demonstrate 11 junctions working as intended, using a low density cold atom cloud with as little as one atom on average in any one junction. Our device opens new possibilities for engineering quantum states of matter and light on a microscopic scale.Micro-fabricated chips are widely used to control clouds of ultra-cold atoms and BoseEinstein condensates [3,4]. Recently, the idea has been extended to the control of ions [5] and similar possibilities exist for molecules [6]. This atom-chip technology provides a way to miniaturise existing atomic physics devices. In addition, it promises new devices that take advantage of the elementary quantum nature of atoms [7][8][9] [16][17][18] or otherwise attached [19] to a chip. A pair of these fibres looking into each other can be used to detect an atom cloud and can reach close to single atom sensitivity [17]. When reflective coatings are added, the gap between two fibres [1,20] or between one fibre and a micro-fabricated mirror [21] becomes a Fabry-Perot resonator. Similarly, a fibre can be coupled to a micro-disk resonator [22,23]. These devices can achieve strong atom-photon coupling for applications in quantum information processing.This letter reports a further order of magnitude scale reduction, in which the 125 µm-diameter optical fibre is replaced by an integrated waveguide only 10 µm across, with a 4 µm square core. Since a BEC is typically ∼ 100 µm long, this size reduction opens the new 3 possibility of intersecting a BEC with many closely spaced atom-photon junctions of high coupling strength. In our device, illustrated in Figure 1, a trench containing the cold atoms cuts through an array of 12 waveguides spaced by 10 µm. This design is a significant advance in the way that photons can be coupled to ultracold atoms.In order to characterise the chip, we have released cold atoms into a junction to measure its sensitivity and to demonstrate the basics of its operation. Every few seconds, 87 Rb atoms are cooled and collected from a room-temperature vapour by a Low-Velocity Intense Source (LVIS), then transferred to a magneto-optical trap (MOT) about 4 mm from the chip surface, where the atom density is up to 4 × 10 −2 atoms/µm 3 and the temperature is ∼ 100µK. We push this cloud towards the chip just before switching off the MOT light and magnetic field, thereby launching the atoms at 40 cm/s into the trench. The light beams from the waveguides diverge only slightly as they cross the trench, with w -the 1/e radius of the field -growing from 2.2 µm to 2.8 µm. Since the width of the trench is L = 16 µm, any given beam interacts with roughly one to four atoms of the cloud as they pass through.Each atom crosses the light in ∼ 7 µs, scattering up to 130 photons (the fully saturated rate is Γ/2 = 1.9 × 10 7 s −1 ).Wi...

Prospects for using integrated atom-photon junctions for quantum information processing

“…2 Because this shift is much larger than the power-broadened linewidth (i.e. greater than both the excited-state natural linewidth and the Rabi frequency for excitation), the excitation of a second atom to the Rydberg state is suppressed by being off-resonant.…”

“…We have recently demonstrated detection of cold atoms using multiple channels of a monolithic optical waveguide chip [2], and we will take these already-proven structures as a basis for application to QIP. Light is brought to and from the chip by optical fibres (not shown).…”

“…A trench cut into the silica completes the atom-photon junctions, as described in Ref. [2]. The whole chip is glued onto a macroscopic copper structure, which carries the current for magnetic and magneto-optical trapping The device we consider is a microfabricated optical chip integrated together with a current-carrying chip for magnetic trapping and evaporative cooling (see Fig.…”

Contactless nonlinear optics mediated by long-range Rydberg interactions

“…If tailored to imprint uniform phase shifts, the micron-scale interaction length provides a convenient starting point for scalable all-optical QIP 15,17 based on tweezer arrays 28 or coupled to optical circuits in integrated photonic waveguides 29 . Quantum simulators based on dipolar interactions, for example, of spin models 30 or nonradiative energy transfer 31 , may now be realized with photons stored as collective Rydberg excitations, providing the added benefit of fast coherent read-out and the ability to measure both amplitude and phase.…”

Optimal preparation of quantum states on an atom-chip device

“…Very recently, they have been also applied to the realization of atom interferometers based on non-classical motional states [6]. Furthermore, atom chips can be integrated with nanostructures [7], or photonic components [8], to implement new quantum information processing tools, or used as novel platforms for quantum simulations [9] and controllable coherent dynamics [10].As in most quantum technological applications, the ability to quickly and faithfully prepare arbitrary input states is of utmost importance. In particular, it is essential to speedup the initialization protocol of these quantum devices in order to reduce the effects of the inevitably present noise and decoherence sources.…”