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.
Multiphoton Processes Limit Precision in Quantum System Control
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.
Svetlana Malinovskaya, professor at Charles V. School of Engineering and Science
Digitized Laser Pulses Enable Controlled Quantum State Transfer
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.
Svetlana Malinovskaya, professor at Charles V. School of Engineering and Science
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