Abstract
The conventional approach to perform two-qubit gate operations in trapped ions relies on exciting the ions on motional sidebands with laser light, which is an inherently slow process. One way to implement a fast entangling gate protocol requires a suitable pulsed laser to increase the gate speed by orders of magnitude. However, the realization of such a fast entangling gate operation presents a big technical challenge, as such the required laser source is not available off-the-shelf. For this, we have engineered an ultrafast entangling gate source based on a frequency comb. The source generates bursts of several hundred mode-locked pulses with pulse energy $\sim$800 pJ at 5 GHz repetition rate at 393.3 nm and complies with all requirements for implementing a fast two-qubit gate operation. Using a single, chirped ultraviolet pulse, we demonstrate a rapid adiabatic passage in a Ca$^+$ ion. To verify the applicability and projected performance of the laser system for inducing entangling gates we run simulations based on our source parameters. The gate time can be faster than a trap period with an error approaching $10^{-4}$.
Highlights
Trapped atomic ions are a well-known resource for testing and implementing quantum-information and quantumcomputation protocols [1,2,3,4,5]
The difficulty lies in achieving a higher repetition rate ( 1/trap period) and sufficiently high pulse energy to enable state-dependent kicks, while restricting the wavelength range to a specific narrow-band ultraviolet spectrum
We found that the booster optical amplifiers (BOAs) was responsible for these anomalies because the carrier injection and recombination time of such amplifiers is similar to the 200-ps pulse period [23] of the pulse train
Summary
Trapped atomic ions are a well-known resource for testing and implementing quantum-information and quantumcomputation protocols [1,2,3,4,5]. There are ongoing efforts to develop high average power and high repetition rate, ultrafast UV and extreme-UV laser sources [14,15,16,17,18] for a range of applications and for quantum computation to expedite entangling gates in trapped ions [19]. In the latter, the difficulty lies in achieving a higher repetition rate ( 1/trap period) and sufficiently high pulse energy to enable state-dependent kicks, while restricting the wavelength range to a specific narrow-band ultraviolet spectrum. Both cavities are locked to an auxiliary continuous-wave laser, which in turn is locked to a mode of the frequency comb as detailed in Ref. [22]
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