BLOGS

High-dimensional quantum transport enabled by nonlinear detection. In our concept, information is encoded on a coherent source and overlapped with a single photon from an entangled pair in a nonlinear crystal for up-conversion by sum frequency generation, the latter acting as a nonlinear spatial mode detector. The bright source is necessary to achieve the efficiency required for nonlinear detection. Information and photons flow in opposite directions: one of [the] Bob’s entangled photons is sent to Alice and has no information, while a measurement on the other in coincidence with the upconverted photon establishes the transport of information across the quantum link. Alice need not know this information for the process to work, while the nonlinearity allows the state to be arbitrary and unknown dimension and basis. Credit: Nature Communications (2023). DOI: 10.1038/s41467-023-43949-x

Topics: Applied Physics, Computer Science, Cryptography, Cybersecurity, Quantum Computers, Quantum Mechanics, Quantum Optics

Nature Communications published research by an international team from Wits and ICFO- The Institute of Photonic Sciences, which demonstrates the teleportation-like transport of "patterns" of light—this is the first approach that can transport images across a network without physically sending the image and a crucial step towards realizing a quantum network for high-dimensional entangled states.

Quantum communication over long distances is integral to information security and has been demonstrated with two-dimensional states (qubits) over very long distances between satellites. This may seem enough if we compare it with its classical counterpart, i.e., sending bits that can be encoded in 1s (signal) and 0s (no signal), one at a time.

However, quantum optics allow us to increase the alphabet and to securely describe more complex systems in a single shot, such as a unique fingerprint or a face.

"Traditionally, two communicating parties physically send the information from one to the other, even in the quantum realm," says Prof. Andrew Forbes, the lead PI from Wits University.

"Now, it is possible to teleport information so that it never physically travels across the connection—a 'Star Trek' technology made real." Unfortunately, teleportation has so far only been demonstrated with three-dimensional states (imagine a three-pixel image); therefore, additional entangled photons are needed to reach higher dimensions.

'Teleporting' images across a network securely using only light, Wits University, Phys.org.

Atomic analog: when a beam of light is shone into a water droplet, the light is trapped inside. (Courtesy: Javier Tello Marmolejo)

Topics: Modern Physics, Optics, Quantum Mechanics, Quantum Optics, Research

Light waves confined in an evaporating water droplet provide a useful model of the quantum behavior of atoms, researchers in Sweden and Mexico have discovered. Through a simple experiment, a team led by Javier Marmolejo at the University of Gothenburg has shown how the resonance of light inside droplets of specific sizes can provide robust analogies to atomic energy levels and quantum tunneling.

When light is scattered by a liquid droplet many times larger than its wavelength, some of the light may reflect around the droplet’s internal edge. If the droplet’s circumference is a perfect multiple of the light’s wavelength inside the liquid, the resulting resonance will cause the droplet to flash brightly. This is an optical example of a whispering gallery mode, whereby sound can reflect around a circular room.

This effect was first described mathematically by the German physicist Gustav Mie in 1908 – yet despite the simplicity of the scenario, the rich array of overlapping resonances it produces can create some incredibly complex patterns, some of which have yet to be studied in detail.

Optical Tweezers

To explore the effect in more detail, Marmolejo and the team devised an experiment where they confined water droplets using optical tweezers. They evaporated the liquid by heating it with a fixed-frequency laser. As the droplets shrank, their circumferences will sometimes equal a multiple of the laser’s wavelength. At these “Mie resonances,” the droplets flashed brightly.

As they studied this effect, the researchers realized that the flashing droplets are analogous to the quantum behaviors of atoms. In these “optical atoms,” orbiting electrons are replaced with resonating photons. The electrostatic potential that binds electrons to the nucleus is replaced by the droplet’s refractive index, which tends to trap light in the droplet by internal reflection. The quantized energy levels of an atom are represented by the droplet sizes where Mie resonances occur.

Flashing droplets could shed light on atomic physics and quantum tunneling, Sam Jarman, Physics World.

This calculated diffraction image shows how forked diffraction gratings shape the atoms' wave function into a vortex. (Courtesy: Science/AAAS)

Topics: Bose-Einstein Condensate, Nanotechnology, Particle Physics, Quantum Optics

A wave-like property previously only seen in beams of light and electrons has been observed for the first time in atoms and molecules. By passing beams of helium and neon through a grid of specially shaped nanoslits, researchers led by Edvardas Narevicius of Israel’s Weizmann Institute of Science succeeded in giving the beams a non-zero orbital angular momentum (OAM). The resulting structures are known vortex beams, and they could be used for fundamental physics studies such as probing the internal structure of protons.

Many natural systems contain vortices – think of tornadoes and ocean eddies on Earth, the red spot on Jupiter, and gravitational vortices around black holes. On all scales, such vortices are characterized by the circulation of a flux around an axis. In the quantum world, these swirling structures are found in ensembles of particles that can be described by a wavefunction, including superfluids and Bose-Einstein condensates.

Atoms and molecules make vortex beams, Isabelle Dumé, Physics World

Artist’s impression of UQ’s new quantum microscope in action. Credit: The University of Queensland

Topics: Biology, Biotechnology, Instrumentation, Quantum Mechanics, Quantum Optics

In a major scientific leap, University of Queensland researchers have created a quantum microscope that can reveal biological structures that would otherwise be impossible to see.

This paves the way for applications in biotechnology, and could extend far beyond this into areas ranging from navigation to medical imaging.

The microscope is powered by the science of quantum entanglement, an effect Einstein described as “spooky interactions at a distance.”

Professor Warwick Bowen, from UQ’s Quantum Optics Lab and the ARC Centre of Excellence for Engineered Quantum Systems (EQUS), said it was the first entanglement-based sensor with performance beyond the best possible existing technology.

“This breakthrough will spark all sorts of new technologies — from better navigation systems to better MRI machines, you name it,” Professor Bowen said.

“Entanglement is thought to lie at the heart of a quantum revolution. We’ve finally demonstrated that sensors that use it can supersede existing, non-quantum technology.

“This is exciting — it’s the first proof of the paradigm-changing potential of entanglement for sensing.”

Major Scientific Leap: Quantum Microscope Created That Can See the Impossible, University of Queensland