Quantum Tech

University Kaiserslautern fast tracks quantum computer development

12th June 2024
Paige West

There are various methods for constructing a Quantum Computer (QC), and RPTU Kaiserslautern's approach within the Rymax One collaboration involves creating an array of single atoms that function as qubits.

The primary challenge lies in precisely positioning and maintaining each atom. This is achieved by using a laser to trap each atom at the centre of the beam, effectively acting as an optical tweezer. However, programming each movement of the beam point-by-point currently requires extensive programming and generates a substantial amount of data.

This process has been significantly streamlined with the introduction of the new Direct Digital Synthesis (DDS) firmware option from Spectrum Instrumentation. The DDS firmware allows the position of the lasers to be controlled with a few simple commands that define the start and stop parameters, eliminating the need for time-consuming, large data array calculations.

Furthermore, in the next phase, they will use the AWGs to shape ideal UV laser pulses for precisely controlling interactions between qubits.

“DDS has become a vital tool in our project, and we are finding that it can actually be used in other things in the lab as it is very flexible and can be used for other functions so we don’t have to buy dedicated equipment for them. For example, pulsed lasers, chirp generation, etc. We worked very closely with Spectrum to develop this DDS feature and are now working on expanding its possible uses in research so that it can help other laboratories.”

He added that Spectrum AWG cards were chosen because they are becoming the preferred solution for quantum research, thanks to their excellent analogue performance, large memory, and high transfer speed. The latter is particularly crucial as experiments must pause until the re-ordering waveforms are computed and uploaded onto the cards. The superior transfer speed of Spectrum AWG cards distinguishes them from other products, making them widely used in the AMO/QC community. Additionally, the speed of the cards' operation is vital. Fast AWGs often face issues with latencies of tens of milliseconds or large jitter, leading to inaccuracies and longer processing times as the system repeatedly corrects errors. The DDS firmware allows Spectrum’s AWGs to generate commands within twenty microseconds, and due to their intrinsic timing, these commands are practically jitter-free.

In one experiment, the Spectrum Instrumentation AWG card M4i.6631-x8 was used to drive an Acousto-Optic Deflector (AOD) that generates a tweezer to trap atoms. The AOD was driven by an RF signal with a frequency of around 82MHz. In their current setup, a 1MHz change moves the tweezer with an atom by about 8μm within 100μs, utilising s-shaped frequency ramps to minimise heating. During this process, the signal's amplitude is linearly adjusted to compensate for changes in light intensity.

The DDS firmware option

Direct Digital Synthesis (DDS) is a method for generating arbitrary periodic sine waves from a single, fixed-frequency reference clock, widely used in various signal generation applications. The new option from Spectrum Instrumentation allows users to define 23 DDS cores per AWG card, which can be routed to the hardware output channels. Each DDS core (sine wave) can be programmed for frequency, amplitude, phase, frequency slope, and amplitude slope. The DDS output can be synchronised with external trigger events or by a programmable timer with a resolution of 6.4ns.

In DDS mode, the AWG acts as a generator for the multi-tone DDS signal. The unit’s built-in 4GByte memory and fast DMA transfer mode enable the streaming of DDS commands at a rate of up to 10 million commands per second. This unique capability offers the flexibility to perform user-defined slopes (e.g., s-shaped) and various modulation types (e.g., FM and AM) with simple, easy-to-use DDS commands.

The Rymax One QC design

Since 2021, Spectrum Instrumentation and the University of Kaiserslautern have been part of the BMBF (German Federal Ministry of Education and Research) funding programme, ‘Quantum Technologies – From Basic Research to Market’, within the Rymax One consortium. The consortium aims to build a Quantum Optimiser. For this purpose, individual Ytterbium atoms are suspended in a vacuum in a Rydberg state using optical tweezers. The Rymax collaboration specifically focuses on quantum optimisation problems, such as the Maximum Independent Set problem, and algorithms like QAOA or quantum annealing to find solutions. This approach enables the development of optimised hardware for ‘analogue’ quantum computing. A key aspect of the design is dynamic control over UV laser light, which requires full control over various RF signals. This is where Spectrum Instrumentation’s extensive expertise is invaluable.

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