Computer based arbitrary waveform generator aids quantum research
Precision is always important in research and there can be few research areas needing greater precision than that of quantum research. For the example applications described below, a versatile programmable Arbitrary Waveform Generator (AWG) was required to generate multiple frequency signals of varied shape.
Who is the customer?
The Institute for Quantum Optics and Quantum Information,University of Innsbruck, Austria.
There are in fact two application areas; radio frequency domain and destructive interference.
Radio Frequency Domain
A multiple-frequency signal needs to be generated and applied for this regime, each frequency component using a sinusoidal function. The resulting beat signal is used to simultaneously address individual ions in a trapped-ion quantum simulator. The ion trap is shown Figures 1 and (close up) in 2. Christine Maier, a researcher at the Institute, explains, "We are doing the quantum simulation with trapped, cooled calcium ions, for which single-ion addressability is essential. To achieve this, we send a laser beam through an acousto-optic deflector (AOD). The frequency of the radio frequency signal, which one applies to this AOD crystal, defines the deflection angle of the laser beam and therewith it decides which ion of our linear ion string is addressed."
The second application is the cancellation, via destructive interference, of undesired frequency mixing terms that arise, for example, when applying multiple-frequency signals to an acousto-optic modulator. As Christine Maier says: "Applying RF signals to acousto-optic crystals is a basic technique in our laboratories," she adds. "When applying multiple-frequency signals, several sum- and difference- frequency components will arise and finally map onto the optical signal that you are sending onto the ions. This brings two problems. First, you lose power from the frequency components that you actually want and second, the mixing terms could hit some resonance of the ion chain and destroy the quantum model that you want to simulate.
Requirements of the customer
An easy to program AWG to produce multiple-frequency signals, each having arbitrary amplitudes, so that the output could be easily customised.
Radio Frequency Domain
The M4i.6631-x8 AWG produces multiple-frequency signals, each having arbitrary amplitudes. This allows multiple ions to be address in the ion string simultaneously. One advantage of this is that the experiment is faster without the need to cycle through addressing each ion individually, one after the other. It also opens up an entirely new field of study for the researchers: up to now they could only investigate unperturbed energy transport in the ion chain. However, by addressing individual ions with arbitrary strength, they can now can create arbitrary potential barriers and study energy transport in disordered quantum systems. The AWG even allows them to program time-varying potentials to study dynamic disorder phenomena.
Using the M4i.6631-x8 AWG enables the researchers to cancel the undesired effects of loss of power and resonance, using destructive interference, in real-time measurement and feedback loops. It was important to have an AWG that could easily be programmed using a standard PC, so that the output could be easily customised to the requirement.
"It is highly configurable," adds Christine. "Two AWG channels, a choice of trigger options, external clock inputs, multiple and gated replay modes, looping functions and even the possibility to combine two trigger inputs via logic gates. This combined with the high resolution and a sampling rate of 1.25 GS/s made it the logical choice to provide the flexibility for the projects that we have now and importantly, whatever needs we may have in the future with just one instrument."
© Spectrum Instrumentation GmbH 29.09.17