Visualizing the mysterious dance: Quantum entanglement of photons captured in real-time

In collaboration with Danilo Zia and Fabio Sciarrino from Sapienza University of Rome, researchers at the University of Ottawa recently showcased a novel technique that makes it possible to visualize the wave function of two entangled photons—the fundamental particles that make up light—in real-time.

To put it another way, the idea of entanglement is similar to picking a shoe at random when compared to a pair of shoes. As soon as you recognize one shoe, you can always tell what the other shoe is like—left or right—no matter where in the cosmos it is. The interesting aspect, though, is the inherent ambiguity surrounding the identification process up to the precise observational time.

A fundamental concept in quantum physics, the wave function offers a thorough comprehension of a particle's quantum state. For example, in the shoe example, the shoe's "wave function" may convey data about left or right, size, color, and other attributes.

To put it another way, the wave function lets quantum physicists anticipate what will probably happen when they measure different aspects of a quantum object, including location, velocity, etc.

This capacity to forecast the future is extremely significant, particularly in the quickly developing field of quantum technology, where it is possible to test the computer itself by understanding the quantum state that is created or input into a quantum computer. Furthermore, the quantum states employed in quantum computing are massively multi-entity and very complex, with the potential for substantial non-local interactions (entanglement).

It is difficult to determine the wave function of such a quantum system; this process is called quantum state tomography, or simply quantum tomography. A complete tomography using the conventional methods (which are based on the so-called projective operations) necessitates a high number of measurements, which rises quickly as the system becomes more complicated (dimensionality).

The research group's earlier studies using this method demonstrated that it can take hours or even days to characterize or measure the high-dimensional quantum state of two entangled photons. Furthermore, the quality of the result is largely dependent on the intricacy of the experimental apparatus and is vulnerable to noise.

One way to conceptualize the projective measurement technique to quantum tomography is as viewing shadows of a high-dimensional object projected from separate directions on several walls. A researcher can only see shadows, yet they can nevertheless deduce the form and status of the entire thing from those shadows. For example, in a computed tomography scan (CT scan), a sequence of 2D pictures can be used to reconstruct the information of a 3D object.

But there's another method in classical optics for reconstructing a three-dimensional object. This technique, known as digital holography, works by using a reference light to interfere with the light that an object scatters in order to record a single image known as an interferogram.

The group expanded this idea to the situation of two photons under the direction of Ebrahim Karimi, associate professor in the Faculty of Science, co-director of the uOttawa Nexus for Quantum Technologies (NexQT) research institution, and holder of the Canada Research Chair in Structured Quantum Waves.

It is necessary to overlay a presumed well-known quantum state over a biphoton state in order to reconstruct it, and then to examine the spatial distribution of the locations at which two photons arrive at the same time. A coincidence image is a picture taken of two photons arriving at the same time. These photons might originate from the unidentified source or the reference source. According to quantum physics, it is impossible to pinpoint the photons' source.

As a result, an interference pattern is produced that may be utilized to piece together the wave function that is unknown. A state-of-the-art camera enabling pixel-by-pixel recording of events at nanosecond resolution made this experiment possible.

One of the paper's co-authors, Dr. Alessio D'Errico, a postdoctoral researcher at the University of Ottawa, emphasized the enormous benefits of this novel strategy by saying, "This method is exponentially faster than previous techniques, requiring only minutes or seconds instead of days." Notably, the complexity of the system has no effect on the detection time, which addresses the long-standing scaling issue in projective tomography."

This research has an influence that extends beyond academia. Advancements in quantum technology, including enhanced characterisation of quantum states, quantum communication, and the creation of novel imaging techniques, might be expedited by it.

In Nature Photonics, the research paper "Interferometric imaging of amplitude and phase of spatial biphoton states" was released.