Efficient fluorescence collection from trapped ions with an integrated spherical mirror

Abstract

Efficient collection of fluorescence from trapped ions is crucial for quantum optics and quantum computing applications, specifically, for qubit state detection and in generating single photons for ion-photon and remote ion entanglement. In a typical setup, only a few per cent of ion fluorescence is intercepted by the aperture of the imaging optics. We employ a simple metallic spherical mirror integrated with a linear Paul ion trap to achieve photon collection efficiency of at least 10% from a single Ba + ion. An aspheric corrector is used to reduce the aberrations caused by the mirror and achieve high image quality.With their long coherence time and the straightforward manipulation of internal and external states to store and process quantum information, trapped ions are among the most promising candidates for practical quantum computation [1][2][3]. Coupling of ionic qubits to single photons through spontaneous emission offers an attractive alternative [4] to the more traditional ion trap quantum computing architectures [5,6]. Reliable interconversion between quantum states of single ions and single photons thus becomes one of the most crucial tasks. A robust ion-photon coupling scheme is indispensable for implementing remote quantum gates between ions [7,8] and quantum repeaters [9]. Multi-element refractive optical systems are most widely used for ion and atom fluorescence collection and imaging [10][11][12][13][14][15][16]. Recently, such custom-designed, in-vacuum lenses capable of collecting about 4% of the photons from an ion were used to achieve 0.2% fiber coupling efficiency for 397 nm photons from Ca + [17]. High-finesse optical cavities have also been used [18][19][20] but their full potential has yet to be attained with ions where close proximity of the dielectric cavity mirrors is detrimental to the trapping itself.Simple reflective optics offer an attractive alternative and have been previously implemented in non-imaging fluorescence detectors such as [21]. Compared to their complex refractive counterparts, reflective optics can make large deflection of light propagation with considerably fewer elements and simpler surfaces. Because no transparency is necessary, metallic optical surfaces can be used, which can be placed in close proximity to the ion without affecting the trap performance. Much higher numerical apertures (N.A.) can thus be achieved with comparatively small size optics. Though placing an ion in the focus of a parabolic mirror may be the best scenario [22], and traps designed for such implementation have been successfully demonstrated [23], a high-N.A. parabola is a complicated surface to fabricate, especially in a smallscale device, which would be required for a scalable trapped-ion quantum information processor. Spherical mirrors are much simpler and can be fabricated using standard microelectromechanical systems (MEMS) technology [24]. The intrinsic large image aberrations caused * shugang@u.washington.edu by the spherical mirror can be compensated with optics located outside the ...

The trapping and detection of single atoms using a spherical mirror

“…Moreover, the interaction light can be focused by the same mirror to a tight spot for free space atom-photon coupling. Although spherical mirrors suffer from aberrations, these can be corrected with proper optical elements outside the vacuum chamber [8] and become less significant with decreasing mirror dimensions. For sufficiently small radii of curvature, there can be significant coupling of the light reflected by the mirror into a single-mode fibre [12].…”

Cooling atomic ions with visible and infra-red light

“…Quantum state discrimination between the S 1 2 and D 5 2 levels can be performed using the standard approach using the cooling lasers at 397 nm and 866 nm. The detection probability for a single emitted photon at 397 nm is 0.0028(2), measured by using the ion as a single-photon source, by first shelving and then de-shelving the ion from the D 3 2 level using the 866 nm laser [20]. State detection is performed in a standard window of 350 μs, during which we detect 20 photons for an ion in the S 1 2 level and 0.8 photons for an ion in the D 5 2 level (the latter is primarily due to background scattering from the electrodes of the trap).…”

Efficient collection of single photons emitted from a trapped ion into a single-mode fiber for scalable quantum-information processing

“…Reflective optics is frequently used as an alternative to refractive optics to realize a large NA [32][33][34][35][36][37][38]. A parabolic mirror can perfectly collimate light emitted from a point source and has been studied extensively [36][37][38].…”

“…In that approach, however, the aberrations of the microfabricated mirror cannot be controlled well enough to produce a flat wave front. One important advantage of using a microfabricated mirror compared to a conventional macroscopic mirror [35] is that the geometric aberrations scale as the dimensions of the optics are reduced [48]. The residual OPD is reduced while the wavelength (λ) remains the same, eventually achieving the diffraction limit.…”