The man behind the project, Prof. Dr Matthias Wollenhaupt, who leads the Ultrafast Coherent Dynamics research group at Oldenburg, describes the achievement as a genuine extension of what experimentalists can do. “With our method, we can generate electronic quantum states that have previously only been described theoretically and also make them spatially visible,” he explains. “We have thus expanded the experimental optics toolkit to include a new class of three-dimensional light fields.” That statement captures the essence of the result: for decades, theorists have predicted that fully three-dimensional light fields should enable new forms of quantum control, but creating such fields in the laboratory and using them to steer electrons has remained out of reach until now.

The technical trick at the heart of the experiment lies in the combination of two specially shaped femtosecond laser pulses. Femtosecond pulses are bursts of light lasting only a few millionths of a billionth of a second, so short that within the duration of a single pulse, chemical bonds barely have time to begin vibrating. The researchers used an interferometer to split their laser light into two beams of different colours, shaped each pulse with great precision, and then directed the two beams so that they intersected inside a vacuum chamber at a single point. Where the beams overlapped, their electromagnetic fields added together, producing a three-dimensional interference pattern whose geometry the team could control by adjusting the colours, phases, polarizations and relative timing of the two pulses.

“The fields oscillate in all three spatial directions, opening up new possibilities for investigating and controlling specific light-matter interactions,” explains Darius Köhnke, one of the two lead authors of the study and a PhD student in Wollenhaupt’s group. Conventional laser experiments typically rely on light that oscillates in one or two dimensions, which limits the kinds of quantum states that can be reached. A truly three-dimensional field, by contrast, can drive an electron in ways that no one-dimensional or two-dimensional field can, coupling the electron’s motion along all three axes simultaneously. This is precisely what allows the method to access quantum states that are forbidden or invisible to conventional excitation schemes.

To demonstrate the power of the technique, the team applied their three-dimensional light fields to potassium atoms, a workhorse of atomic physics experiments. They used the fields to selectively excite electrons within the atoms into higher-energy states, known as excited states, and then to release those electrons from the atoms entirely, a process called ionization. The properties of the liberated electrons carry a detailed fingerprint of the quantum states from which they were ejected, allowing the researchers to reconstruct what happened inside the atom. Crucially, by varying the parameters of the light field, they could choose which excited states to populate and which pathways the electrons would follow on their way out.

The experiment also functioned like an ultra-high-speed camera for quantum processes. Because the laser pulses are so short, the researchers were able to observe the changes in the electron states at closely spaced time intervals, capturing successive snapshots of the evolving quantum system. The principle resembles stroboscopic flash photography, in which a rapidly flashing lamp freezes fast motion into a sequence of still images. Stitched together, these snapshots form a movie of the electron states as they evolve under the influence of the three-dimensional field. This time-resolved view is what allowed the team to confirm that the theoretically predicted states were indeed being created and to make their structure spatially visible for the first time.

Beyond its fundamental appeal, the method is particularly promising for one of the most consequential problems in modern chemistry: the detection and control of chiral molecules. Chiral molecules come in two forms that are mirror images of each other but cannot be superimposed, much like a person’s left and right hands. This handedness is not a minor detail. Many biomolecules, including amino acids, carbohydrates and the active ingredients of medicinal products, are chiral, and the two mirror-image forms, called enantiomers, frequently have strikingly different biological effects. The body may metabolize one form beneficially while the other is inert or even harmful.

The dangers of ignoring molecular handedness are written into pharmaceutical history. The active ingredient thalidomide, marketed in the late 1950s and early 1960s under the brand name Contergan, exists in two enantiomeric forms: one causes severe birth defects when taken during pregnancy, while the other is comparatively harmless. Because the two forms are chemically almost identical, separating or distinguishing between them can be extremely difficult, and in the case of thalidomide the drug was sold as a mixture of both. A technique that could reliably sense and even selectively manipulate one handedness over the other would therefore be a powerful tool for drug development, quality control and fundamental biology alike.

Three-dimensional light fields may offer exactly that capability. “Theoretical studies show that three-dimensional light fields can also possess chiral properties,” Wollenhaupt explains. In other words, the light itself can be handed, twisting through space in a way that distinguishes left from right. Such chiral light fields could interact differently with the two enantiomers of a chiral molecule, providing a far more sensitive and selective probe than conventional methods, which typically rely on weak magnetic-dipole effects. The opportunities that three-dimensional light fields open up for investigating and controlling molecular chirality were recently highlighted by physicist Prof. Dr Olga Smirnova of the Max Born Institute for Nonlinear Optics in Berlin in an article published in the journal Science entitled “A New Age of Molecular Chirality”. The Oldenburg team writes that their current study lays an important foundation for such applications, bridging the gap between theoretical proposals and laboratory reality.

The work, reported under the title “Multiphoton ionization with three-dimensional light fields,” signals a broader shift in how physicists think about controlling matter with light. Rather than treating a laser beam as a simple one-dimensional oscillating field, the Oldenburg approach treats the full spatial structure of light as a designable parameter, something to be engineered pulse by pulse in order to write specific quantum states onto atoms and molecules. The same interferometric superposition scheme that produced the new states in potassium atoms can, in principle, be adapted to more complex systems, from chiral molecules in solution to surfaces and nanostructures. If the promise holds, the coming years could see three-dimensional light fields become a standard instrument in the quest to read out, and perhaps even exploit, the handedness of nature at the molecular scale, turning a long-standing theoretical prediction into a practical technology for chemistry, biology and medicine.

Subject of Research: Generation of three-dimensional light fields from superimposed femtosecond laser pulses to control electron quantum states and probe chiral molecules

Article Title: Using three-dimensional light fields to control electrons

Article References: Using three-dimensional light fields to control electrons. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: three-dimensional light fields, femtosecond laser pulses, quantum states, multiphoton ionization, chiral molecules, light-matter interactions, potassium atoms, quantum control, ultrafast optics, chiral sensing, Physical Review Research, University of Oldenburg

John George Francis and Anil Shaji focused on transmon qubits, the workhorse of IBM’s quantum processors and many other superconducting platforms. Transmons are engineered from Josephson junctions and superconducting circuits to be relatively insensitive to charge noise, a design choice that has made them the most widely deployed qubit technology in the world. Yet even the best-fabricated transmons deviate from the idealized textbook description. Stray couplings, higher energy levels, and control imperfections all conspire to make the actual dynamics of the system richer and messier than the standard Hamiltonian predicts.

The team targeted one of the most important operations in the superconducting quantum computing repertoire: the cross-resonance gate. In this scheme, microwaves are applied to a target qubit at the frequency of its control qubit neighbor, creating an entangling interaction that serves as a fundamental building block for two-qubit logic. The cross-resonance interaction has a well-known effective Hamiltonian description, developed in earlier theoretical work, but that description is itself an approximation whose accuracy depends on the details of the hardware and the drive parameters. When the idealized model is used to predict what a real gate does, errors accumulate quickly.

To quantify those errors and correct them, Francis and Shaji turned to real experimental data from ibm_kyiv, one of the processors accessible on the IBM Quantum cloud platform. They collected measurement outcomes for two transmon qubits driven by microwave pulses of varying amplitudes and evolution times, spanning a range of operating conditions. Each data point captured the probabilities of the different computational basis states after the system evolved under the cross-resonance drive, providing a rich empirical fingerprint of the true dynamics that no purely theoretical model could be expected to reproduce exactly.

The heart of their method is a correction operator added to the standard Hamiltonian. Rather than guessing the correction from first principles, the researchers wrote down an ansatz, a flexible mathematical form whose matrix elements are free parameters to be optimized. The goal of the optimization is simple to state and hard to achieve: find the correction terms that make the corrected Hamiltonian’s predicted evolution match the observed hardware data as closely as possible across all the measured amplitudes and times. Because the ansatz is not unique, different parameter choices can yield equally good fits, so the team developed methods to characterize an entire equivalence class of effective corrections rather than a single answer.

Optimizing parameters inside a differential equation is exactly the kind of problem that scientific machine learning was built to solve. The researchers employed adjoint sensitivity analysis, a technique that efficiently computes how the final outcome of a dynamical simulation changes with respect to every parameter in the model, without the prohibitive cost of naive approaches. Combined with gradient descent, this allowed the correction terms to be tuned iteratively until the simulated and measured probability distributions converged. The approach draws on the framework of universal differential equations, in which physical models are embedded in differentiable programs that machine learning tools can optimize end to end.

The results are striking. With the uncorrected Hamiltonian, the worst-case average absolute error in predicting the final measurement probabilities reached 0.48, meaning the theoretical model could be wrong by nearly half a full probability unit, a level of disagreement that would render any gate calibration based on the model unreliable. After the data-driven correction was applied, that worst-case error dropped below 0.05, an improvement of nearly a factor of ten. The corrected Hamiltonian tracked the survival probabilities of all four initial two-qubit states across the full range of pulse amplitudes tested, reproducing the fine structure of the hardware’s time evolution that the standard model missed entirely.

Why does this matter beyond one pair of qubits on one machine? Gate fidelities in today’s quantum processors are limited not only by decoherence but by systematic modeling errors, and as the field marches toward error-corrected, fault-tolerant machines, every fraction of a percent of gate accuracy counts. Accurate Hamiltonian models are also the foundation of optimal control techniques, which design pulse sequences to implement gates as faithfully as possible. If the underlying model is wrong, even the most sophisticated pulse optimization will steer the quantum system to the wrong destination. A data-driven correction loop, in which the model continuously learns from the hardware it describes, offers a path to calibrations that stay faithful as devices drift and age.

The work also highlights a broader shift in how quantum engineers think about the relationship between theory and experiment. Traditional approaches either derive effective Hamiltonians perturbatively from circuit theory or fit a handful of parameters to targeted experiments. The scientific machine learning approach is more ambitious: it treats the Hamiltonian itself as a learnable object, constrained by physics but refined by data, and it embraces the fact that multiple effective descriptions may be equally valid. That equivalence-class perspective is philosophically interesting, but it is also practically useful, because it tells engineers which features of a correction are physically meaningful and which are artifacts of a particular parameterization.

Francis and Shaji’s study, published in Quantum Information Processing, was supported in part by India’s National Quantum Mission and used the high-performance computing facilities at IISER Thiruvananthapuram. The underlying data have been made openly available, allowing other groups to test and extend the method on different hardware platforms. As quantum processors scale to hundreds and eventually thousands of qubits, manual calibration of every interaction will become impossible, and techniques like this one, which let the machine teach itself the physics of its own imperfections, may become as essential to quantum computing as the qubits themselves.

Subject of Research: Data-driven correction of the cross-resonance Hamiltonian of transmon qubits using scientific machine learning

Article Title: Data-driven Hamiltonian correction of transmon qubits

Article References: Francis, J. G., & Shaji, A. (2026). Data-driven Hamiltonian correction of transmon qubits. Quantum Information Processing, 25(10), Article 328. https://doi.org/10.1007/s11128-026-05350-7

Image Credits: AI Generated

DOI: 10.1007/s11128-026-05350-7

Keywords: transmon qubits, Hamiltonian correction, cross-resonance gate, scientific machine learning, IBM Quantum, quantum computing, gradient descent, adjoint sensitivity, quantum control, superconducting qubits, gate fidelity, quantum information processing

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