Stevens team boosts control of quantum states with new laser method

Stevens researchers have devised a method to control quantum systems while avoiding disruptions caused by intense laser fields.

The team reports a solution using a series of precisely timed, low-intensity laser pulses to mimic the effect of a single, powerful burst of light. “Instead of using one very strong laser pulse, we suggest mimicking its effects with a carefully programmed sequence—or train—of weak pulses,” explains Svetlana Malinovskaya, professor at Charles V. School of Engineering and Science. This approach could advance technologies for sensing, computing, and biomedical imaging by enabling more predictable and precise quantum manipulation.A laser’s inherent wave synchronization is critical to its utility in quantum manipulation; unlike broad-spectrum light sources, a laser focuses waves for precise control, as Svetlana Malinovskaya, professor at Charles V. However, intense laser fields introduce a complicating factor: multiphoton processes. These unwanted interactions occur when atoms or molecules absorb multiple photons simultaneously, opening unintended pathways between energy states and disrupting predictable system behavior.Malinovskaya notes that when very strong laser fields are used for precise quantum control, they can also trigger unwanted multiphoton processes, allowing the molecule to access many different states and pathways, making its behavior much more difficult to predict and control. This unpredictability poses a significant challenge for applications demanding extreme precision, such as quantum computing and quantum sensing, where even minor deviations can compromise results.“That’s not what we need, particularly for the precision measurements required in quantum computing or quantum sensing,” Malinovskaya states, emphasizing the need for controlled light-matter interactions. To address this limitation, Malinovskaya and colleagues proposed a “digitized” laser pulse, a series of twelve short, low-intensity pulses calculated to replicate the effect of a single, intense pulse.Their calculations suggest this approach circumvents the problematic multiphoton processes, preventing unwanted excitation of atoms and molecules. Each pulse in the sequence delivers less energy individually, but its timing, intensity, frequency, and phase are all meticulously controlled to achieve the desired quantum manipulation. “By shining laser light on molecules, we can excite molecular vibrations in a controlled way and learn about molecular properties,” Malinovskaya notes, adding that when experimentally demonstrated, this method will open a new way to precisely control quantum systems with weaker laser fields, making it easier to use in practical applications.By shining laser light on molecules, we can excite molecular vibrations in a controlled way and learn about molecular properties.Calculations indicate this approach prevents the problematic multiphoton processes, maintaining control over the quantum system without inducing unintended state changes.

The team’s method achieves equivalent results to stronger pulses while maintaining significantly lower laser intensity at each step, a critical advantage in applications where precise control is paramount. “In those systems, every photon counts,” Malinovskaya emphasizes, highlighting the sensitivity of these quantum interactions.Published in the Journal of the Optical Society of America B, the research detailed in the paper, titled Digitizing ultrafast adiabatic passage with a pulse train, suggests potential benefits for quantum sensors, computers, and simulators, all reliant on the reliable preparation and manipulation of quantum states. This technique may also prove valuable in molecular physics and spectroscopy, where intense laser pulses can otherwise interfere with accurate measurements. The researchers state that the next step will be to test their findings with physical experiments.A laser is a device that creates a very narrow, highly directional beam of light. Source: https://www.stevens.edu/news/stevens-researchers-take-step-toward-more-precise-practical-quantum-technologies See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals.Ivy Delaney has been working with neural networks and machine learning since the mid-nineties, back when a couple of hidden layers and a long afternoon of training counted as ambitious. She has watched the field go from academic curiosity to the thing quietly running underneath everything, and she brings that long view to quantum computing.

For Quantum Zeitgeist she covers the ground where the two fields meet. That means quantum machine learning and the variational algorithms it leans on, and it also means the less glamorous but more interesting story of classical machine learning already doing real work inside quantum machines, decoding error-correcting codes, calibrating noisy hardware and learning the error models that simulators depend on. She writes about the hardware those algorithms have to run on too, and about the post-quantum cryptography scramble that the same hardware has set off. Her stories typically start with the paper, whether that is peer-reviewed work, conference proceedings or an arXiv preprint, with the source linked so you can hold a claim up against the research it came from. She is unimpressed by benchmarks that will not say what they beat, and by demonstrations that only work in the press release.