Digitized Laser Pulse Trains Offer Precise Control of Quantum Systems

Quantum technologies promise to transform medicine, sensing, computing and communications, but they all depend on a delicate feat of engineering: coaxing atoms and molecules into exactly the energy states a researcher wants, and no others. The standard tool for the job is the laser, whose tightly synchronized light waves can nudge quantum systems with extraordinary precision. Yet the very intensity that makes lasers so useful can also be their undoing. Now, researchers at Stevens Institute of Technology and their collaborators have proposed a novel way to sidestep this fundamental tension, using a carefully choreographed sequence of weak laser pulses to achieve what previously demanded a single, powerful blast of light.

The work, led by Svetlana Malinovskaya, professor at the Charles V. Schaefer, Jr. School of Engineering and Science at Stevens, addresses a problem that has long plagued experimentalists working at the frontier of quantum control. “A laser is a device that creates a very narrow, highly directional beam of light,” Malinovskaya explains. “Unlike sunlight or light from regular bulbs or flashlights that scatters in all directions, a laser produces light in which all waves move together in a highly synchronized way allowing the light to be very focused and controlled with remarkable precision.”

When such a light wave reaches a quantum system, its packets of energy, called photons, are absorbed by the atoms and molecules in that system, lifting them into higher-energy states. This is precisely the mechanism by which scientists manipulate quantum behavior. But there is a catch. If the laser field is too intense, a single atom or molecule may interact with several photons at once. These simultaneous interactions, known as multiphoton processes, open additional pathways between the system’s energy levels, scrambling the intended dynamics and rendering the quantum system difficult, sometimes impossible, to predict or control.

“By shining laser light on molecules, we can excite molecular vibrations in a controlled way and learn about molecular properties,” says Malinovskaya. “But 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.” In other words, the instrument of control becomes an instrument of chaos, and the very act of measurement or manipulation contaminates the result.

That unpredictability is more than an inconvenience; it is a roadblock for the technologies hoping to capitalize on quantum mechanics. “That’s not what we need, particularly for the precision measurements required in quantum computing or quantum sensing,” Malinovskaya says. “In those systems, every photon counts.” Quantum computers rely on the faithful preparation and manipulation of quantum states to perform calculations, while quantum sensors extract exquisitely faint signals from their environment, and even a small number of stray photon interactions can corrupt a computation or drown a measurement in noise. The ideal solution would use just enough light to steer a quantum system where it needs to go, without any excess energy spilling over into unwanted channels.

In their new study, Malinovskaya and her collaborators propose to do exactly that with what they describe as a “digitized” laser pulse. Their calculations show that a train of twelve short, low-intensity laser pulses can produce the same net effect on a quantum system as one long, intense pulse, but without pushing the atoms or molecules into the undesirable states that plague high-intensity approaches. The idea is conceptually similar to replacing a single powerful hammer blow with a rapid series of precisely timed taps that, together, accomplish the same task with far less collateral disturbance.

“Instead of using one very strong laser pulse, we suggest mimicking its effects with a carefully programmed sequence—or train—of weak pulses,” Malinovskaya explains. “Each pulse carries much less energy, but its timing, intensity, frequency and phase are precisely calculated and controlled.” According to the team’s analysis, this sequence of gentle nudges can drive the same gradual transfer of a quantum system from one state to another that a much stronger pulse would produce. The desired outcome is preserved, while the laser intensity at each step remains low enough to keep multiphoton processes from ever gaining a foothold.

The method is an outgrowth of a well-established control strategy known as adiabatic passage, in which a quantum system is guided slowly and smoothly between energy states so that it remains stable against small imperfections. By digitizing that smooth evolution into discrete steps, the researchers retain the robustness of the adiabatic approach while shedding its traditional dependence on high peak laser intensities. The result, described in a paper titled “Digitizing ultrafast adiabatic passage with a pulse train” published in the Journal of the Optical Society of America B on September 10, 2026, offers a theoretical blueprint that, if borne out experimentally, could reshape how quantum control experiments are designed across a wide range of platforms.

The potential applications stretch across the quantum technology landscape. Quantum sensors, quantum computers and quantum simulators all depend on reliable preparation and manipulation of quantum states, and the pulse-train technique could make those operations more accurate and repeatable. In molecular physics and spectroscopy, where intense laser pulses often generate background effects that interfere with measurements, the lower-intensity approach could yield cleaner data and sharper insights into molecular structure and behavior. The implications extend beyond physics laboratories as well: in biology and medicine, laser-based technologies are widely used for imaging and disease diagnosis, and reducing pulse intensity offers a straightforward way to minimize damage to sensitive cells and tissues, opening a path to safer optical diagnostics and therapies.

For now, the technique remains theoretical, but the paper lays out all of the necessary calculations in full detail, providing experimenters with a concrete roadmap. “The next step will be to actually test it,” Malinovskaya says. “When demonstrated experimentally, this approach will open a new way to precisely control quantum systems with weaker laser fields, making it easier to use in practical applications.” If the laboratory results match the theory, the digitized pulse train could become a standard tool in the quantum engineer’s kit, helping to bring the promise of quantum technologies—from unimaginably powerful computers to sensors capable of detecting the faintest whispers of nature—closer to everyday reality, one carefully timed pulse at a time.

Subject of Research: Digitized ultrafast adiabatic passage using low-intensity laser pulse trains for precise quantum state control

Article Title: Stevens researchers take step toward more precise, practical quantum technologies

Article References: Stevens researchers take step toward more precise, practical quantum technologies. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: quantum control, laser pulses, multiphoton processes, adiabatic passage, quantum computing, quantum sensing, spectroscopy, molecular physics, quantum states, biomedical imaging, Stevens Institute of Technology, Svetlana Malinovskaya