Ultrafast, high repetition rate, ultraviolet, fiber-laser-based source: application towards Yb^+ fast quantum-logic

Abstract

Trapped ions are one of the most promising approaches for the realization of a universal quantum computer. Faster quantum logic gates could dramatically improve the performance of trapped-ion quantum computers, and require the development of suitable high repetition rate pulsed lasers. Here we report on a robust frequency upconverted fiber laser based source, able to deliver 2.5 ps ultraviolet (UV) pulses at a stabilized repetition rate of 300.00000 MHz with an average power of 190 mW. The laser wavelength is resonant with the strong transition in Ytterbium (Yb⁺) at 369.53 nm and its repetition rate can be scaled up using high harmonic mode locking. We show that our source can produce arbitrary pulse patterns using a programmable pulse pattern generator and fast modulating components. Finally, simulations demonstrate that our laser is capable of performing resonant, temperature-insensitive, two-qubit quantum logic gates on trapped Yb⁺ ions faster than the trap period and with fidelity above 99%.

Scaling Trapped Ion Quantum Computers Using Fast Gates and Microtraps

“…This would result in gate times of 2.5µs. These requirements are consistent with the 300MHz repetition rates, achieved with a laser power of 190mW [44]. There is a linear relationship between π-pulse repetition rate and laser power, hence for a 200MHz repetition rate a laser power of 130mW should be expected.…”

Ultrafast coherent excitation of a 40Ca+ ion

“…It has been proposed that two-qubit entangling gates with gate times of less than one trap period should be realizable by making the ions interact with counter-propagating ultrafast laser pulses [13]. Several groups are working on its realization [14,15] but so far only single-qubit gate operations [16,17] and single-ion spinmotion entanglement [18] have been reported on time scales shorter than the ion oscillation period. Creation of two-qubit entanglement by a train of ultrafast laser pulses within a few microseconds has been demonstrated in the ground-states of a pair of Yb + ions [19].…”

A Study on Fast Gates for Large-Scale Quantum Simulation with Trapped Ions

“…For this square pulse this rotational infidelity is approximately  414243. Pulses within each pulse pair are assumed to have a relative phase of π - this means there is no residual population transfer between the 0 and 1 states, even with imperfect pulse area, helping to reduce gate error from pulse imperfections3241. Such a phase shift would be easily possible in an experiment using simple optics.…”

“…High-performing gates require rotational fidelities on the order of 10 −6 and decoherence rates below 10 s −1 . If these requirements are satisfied, it appears that fast gates can significantly outperform MS gates in terms of gate time, and can be implemented with very high fidelity if high-repetition-rate lasers are available323951525354. Therefore, fast gates hold significant promise for the future of trapped ion quantum simulation and quantum information processing.…”