Dear quanta,

Tomorrow we will meet at 11am in 6-310 and go around the room and give updates. This will be our last group meeting for the semester.

In the afternoon we will have a talk which gives a sense of how up for grabs the basic categories of quantum computers still are.

Friday, Dec 13, 2019, 1:30pm, 6C-442

Laser-free trapped-ion quantum logic using an oscillating magnetic field gradient at radio frequency

Raghavendra Srinivas (NIST & U.C. Boulder)

Trapped-ion quantum logic is usually performed using laser-induced coupling of the ions’ internal spin states to their motion. Laser-free spin-motion coupling methods, which eliminate photon scattering errors and offer benefits for scalability, have been proposed and demonstrated using static magnetic field gradients or magnetic field gradients oscillating at GHz frequencies [1-4]. We present a new method of spin-motion coupling for trapped ions without lasers, instead using microwaves and a magnetic field gradient oscillating at radio frequency [5]. We demonstrate and characterize this method with trapped Mg+ ions, cooling a single mode of motion to close to its ground state, and generating entangled states of two ions. This implementation offers important technical advantages over other laser-free techniques, while also enabling laser-free entangling gates with reduced sensitivity to qubit frequency errors [6]. These experiments are performed in a surface-electrode trap that incorporates current-carrying electrodes to generate the microwave fields and the oscillating magnetic field gradient.  Currently, we achieve a Bell-state fidelity of 0.996(2) with ground-state-cooled ions and 0.991(3) for ions cooled to the Doppler limit (nbar = 2).

[1] Mintert and Wunderlich PRL 87, 257904 (2001)
[2] Weidt et al. PRL 117, 220501 (2016)
[3] Ospelkaus et al. Nature 476, 181 (2011)
[4] Harty et al. PRL 117, 140501 (2016)
[5] Srinivas et al. PRL 122, 163201 (2019)
[6] Sutherland et al. NJP 21, 033033 (2019)