Physicists at the University of Warsaw and the University of Ottawa successfully split a single photon into an improbable, multi-particle state, according to a study published this week in the journal Nature Photonics. The experiment demonstrates a method for controlling quantum light, potentially advancing secure data transmission and quantum computing architectures.
Splitting the Quantum Unit
In quantum mechanics, a photon is typically treated as an indivisible fundamental particle of light. However, the international research team, led by Dr. Michał Karpiński, utilized a specialized process involving a nonlinear crystal to manipulate the photon’s wave function. By passing a single photon through a system designed for “quantum state engineering,” the researchers forced the photon to exist in a superposition of different particle numbers simultaneously.
The resulting state—described by the researchers as a “mixture from zero to infinity”—refers to the photon’s ability to fluctuate between having no particles and an indefinite, theoretically infinite number of particles. This is not a division in the classical sense of breaking a physical object into pieces. Instead, it is a manipulation of the photon’s quantum field, allowing it to occupy a complex state that includes multiple particle counts at the same time. This phenomenon relies on the fundamental principles of quantum field theory, where particles are viewed as excitations of underlying fields. By engineering these excitations, the team has pushed the boundaries of how light can be structured at the most granular level.
In the standard model of quantum optics, a single photon is defined by a specific Fock state, representing a single excitation in a specific mode of the electromagnetic field. The work published in Nature Photonics challenges the rigid constraints of these Fock states, effectively creating a superposition that spans different Fock states. This is theoretically significant because it demonstrates that the “identity” of a photon—its particle number—can be treated as a variable rather than a fixed constant.
Methodology and Experimental Setup
The team employed a technique known as “quantum pulse gate” technology. This allows for the precise temporal and spectral shaping of light. By applying this gate to a single-photon source, the researchers could effectively “split” the energy distribution of the photon into a swarm of particles that behaved as a single, coherent quantum system.
According to the study, the experiment achieved high-fidelity control over these states, which were verified using homodyne detection—a method for measuring the phase and amplitude of light waves. The results confirm that the photon maintained quantum coherence throughout the process, a necessary condition for any practical application in quantum information science. Homodyne detection is a standard practice in quantum optics, relying on the interference of an unknown signal with a strong local oscillator beam to extract the quadrature components of the light field.
The experimental setup required extreme precision to ensure that the nonlinear crystal—typically a material like periodically poled lithium niobate—interacted with the photon in a way that induced the desired transformation without destroying the quantum information. The challenge of such experiments lies in maintaining the delicate quantum phase relationships, which are easily disrupted by external noise or thermal fluctuations.
Implications for Quantum Communications
The ability to generate and manipulate these “particle swarms” offers a new pathway for quantum key distribution (QKD) and secure communication networks. Traditional QKD relies on the unique properties of individual photons to ensure security; if an eavesdropper attempts to intercept the transmission, the state of the photon is altered, revealing the intrusion. By moving toward multi-particle states, researchers are exploring high-dimensional quantum states, which are more robust against certain types of noise and allow for the encoding of more information per photon.
The researchers suggest that by using a multi-particle state, the information capacity of a single quantum channel could be significantly increased. Because the state involves a superposition of particle numbers, it provides a larger “alphabet” for encoding data compared to the binary states currently used in fiber-optic quantum communications. In current QKD protocols like BB84, information is typically encoded in the polarization or phase of single photons, limiting the data density to a few bits per photon. This new approach could potentially expand this capacity into the realm of qudits—quantum states with more than two levels.
Future Research and Uncertainty
While the laboratory results are verified, the transition from a controlled vacuum environment to real-world fiber networks remains a significant hurdle. Dr. Karpiński noted that the primary challenge moving forward is mitigating the effects of decoherence, which occurs when the quantum system interacts with its surrounding environment. Decoherence is the process by which quantum systems lose their superposition and entanglement due to interaction with the external environment, such as temperature variations, vibrations, or impurities in optical fibers.
The team plans to focus their next phase of research on increasing the distance over which these multi-particle states can be transmitted. As of June 17, 2026, the experiment remains a proof-of-concept, establishing a new framework for light-matter interaction that researchers believe will serve as a foundation for future quantum-optical devices. Whether this method can be scaled for commercial infrastructure remains a question for future peer-reviewed trials. The scientific community often views such breakthroughs as essential steps toward the “Quantum Internet,” a vision of networked quantum computers that share information via entangled particles rather than traditional electronic pulses.
Scaling this technology requires overcoming the limitations of current fiber-optic infrastructure, which is optimized for classical, high-intensity signals rather than single-photon quantum states. Researchers must develop better quantum repeaters—devices that can extend the range of quantum signals—to prevent the signal attenuation that naturally occurs over long distances in glass fibers. The successful manipulation of light demonstrated by the Warsaw and Ottawa teams provides a technical roadmap for how such sophisticated quantum states might one day be generated and processed on a larger, more reliable scale.
