Integrated optical addressing of an ion qubit

Abstract

The long coherence times and strong Coulomb interactions afforded by trapped ion qubits have enabled realizations of the necessary primitives for quantum information processing (QIP) 1 , and indeed the highest-fidelity quantum operations in any qubit to date 2-4 . But while light delivery to each individual ion in a system is essential for general quantum manipulations and readout, experiments so far have employed optical systems cumbersome to scale to even a few tens of qubits 5 . Here we demonstrate lithographically defined nanophotonic waveguide devices for light routing and ion addressing fully integrated within a surface-electrode ion trap chip 6 . Ion qubits are addressed at multiple locations via focusing grating couplers emitting through openings in the trap electrodes to ions trapped 50 µm above the chip; using this light we perform quantum coherent operations on the optical qubit transition in individual 88 Sr + ions. The grating focuses the beam to a diffraction-limited spot near the ion position with a 2 µm 1/e 2 -radius along the trap axis, and we measure crosstalk errors between 10 −2 and 4×10 −4 at distances 7.5-15 µm from the beam center. Owing to the scalability of the planar fabrication employed, together with the tight focusing and stable alignment afforded by optics integration within the trap chip, this approach presents a path to creating the optical systems required for large-scale trapped-ion QIP.Individual trapped ions show great promise for quantum computing; however, the lack of a scalable optical interface to manipulate and measure the quantum states of ions has been a major limitation to the development of a large-scale system 5 . Our approach to this problem utilizes nanophotonic single-mode (SM) waveguides and grating couplers integrated within the trap chip. Light is routed on chip by the waveguides and coupled by the gratings to beams with designed amplitude and phase profiles emitting from the chip towards the ions. These gratings are compact compared to the optical fibers and Fresnel lenses (both with cross-sections ≥100 µm in diameter) previously integrated with planar traps for addressing 7 and fluorescence collection 8,9 , and most importantly the planar fabrication used here to define the optics for both routing and addressing lends itself to intimate integration with the trap electrodes. Furthermore, such waveguide systems have been demonstrated to be scalable to complex geometries of thousands of devices or more 10 . Though micro-electro-mechanical systems (MEMS) mirrors integrated with traps have been proposed as well 11 , experiments so far have utilized MEMS components external to the vacuum chamber and separate from the chip 12 , leaving full integration an essential outstanding challenge.Integrated waveguide devices bring several advantages for ion addressing in planar traps. The ability to fabricate, in the same lithographically defined waveguide layer, multiple splitters, waveguide crossings, and bends with radii less than 10 µm, would enable the realization of a v...

Probing surface charge densities on optical fibers with a trapped ion

“…Such fields have been found to be correlated to ion heating [15]. Efforts are also underway to integrate optical elements required to address ions with laser beams [21], to collect ions' fluorescence [20,23,27], or to build fiber-based cavities [25,44]. While these elements are fixed with respect to the ion trap, more complex future tasks, such as selective addressing or imaging, may benefit from movable mirrors, lenses, fibers, or waveguides placed close to ions.…”

“…In contrast, only a few studies have been undertaken on dielectrics close to trapped ions [18]. However, the question of dielectric surface interactions with ions is highly relevant, as the integration of optics into microtraps is expected to enable the scalable and efficient initialization, manipulation, and measurement of ion-based quantum bits [19], as demonstrated in recent proof-of-principle experiments, e.g., with Fresnel lenses, waveguides, and high-finesse optical cavities [20,21,22]. Materials like indium tin oxide (ITO) open up the possibility to produce transparent electrodes [23], but they also introduce optical losses precluding their use in high-finesse cavities.…”

Multilayer ion trap technology for scalable quantum computing and quantum simulation

“…Conventionally, in surface-electrode ion traps all electrodes are built in a single plane by standard microfabrication techniques [10]. First integration of key scalable elements into a single layer chip such as micro-optical components [11], nanophotonic waveguide devices [12] or microwave conductors (MWC) [13] have been demonstrated. However, interconnecting separated components built in this system imposes new challenges on trap design where signal lines have to be routed around other elements.…”

Simulating the performance of a distance-3 surface code in a linear ion trap

“…Note that we have omitted errors introducing ion crosstalk during individual ion addressing. This is because systems can be built to minimize this effect and control sequences exist that can reduce the effect of such errors [109][110][111][112].…”