Arbitrary waveform generator precise enough for quantum research

June 06, 2017 // By Greg Tate
Precision is always important in research and there can be few research areas needing greater precision than that of quantum research. The Institute for Quantum Optics and Quantum Information at the University of Innsbruck, Austria needed an Arbitrary Waveform Generator (AWG) to generate a wide variety of signals for their research.

The first application is applying a multiple-frequency signal in the radio frequency regime. Each frequency component is realised using a sinusoidal function.  The resulting beat signal is used to simultaneously address individual ions in a trapped-ion quantum simulator.

Fig. 1: Ion trap

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 AWG now allows us to produce multiple-frequency signals, even with each having arbitrary amplitudes, which means that we can now address multiple ions in our ion string simultaneously.

One advantage of this is that the experiment is faster because we don't need to cycle through addressing each ion individually, one after the other.  But it also opens up an entirely new field of study for us: up to now we could only investigate unperturbed energy transport in our ion chain. However, by addressing individual ions with arbitrary strength means that we now can create arbitrary potential barriers and study energy transport in disordered quantum systems. The AWG even allows us to program time-varying potentials to study dynamic disorder phenomena.”

Fig. 2: Ion string.

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. “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 frequencies of the ion chain and destroy the quantum model that you want to simulate.  Using the AWG enables us to cancel these undesired terms via destructive interference in real-time measurement and feedback loops.”

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