Strategic Communications and Marketing News Bureau

‘Superdense’ coding gets denser

Paul Kwiat, a John Bardeen Professor of Physics and Electrical and Computer Engineering, has broken the record for the most amount of information sent by a single photon.

Paul Kwiat, a John Bardeen Professor of Physics and Electrical and Computer Engineering, has broken the record for the most amount of information sent by a single photon.

CHAMPAIGN, Ill. – The record for the most amount of information sent by a single photon has been broken by researchers at the University of Illinois. Using the direction of “wiggling” and “twisting” of a pair of hyper-entangled photons, they have beaten a fundamental limit on the channel capacity for dense coding with linear optics.

“Dense coding is arguably the protocol that launched the field of quantum communication,” said Paul Kwiat, a John Bardeen Professor of Physics and Electrical and Computer Engineering. “Today, however, more than a decade after its initial experimental realization, channel capacity has remained fundamentally limited as conceived for photons using conventional linear elements.”

In classical coding, a single photon will convey only one of two messages, or one bit of information. In dense coding, a single photon can convey one of four messages, or two bits of information.

“Dense coding is possible because the properties of photons can be linked to one another through a peculiar process called quantum entanglement,” Kwiat said. “This bizarre coupling can link two photons, even if they are located on opposite sides of the galaxy.”

Using linear elements, however, the standard protocol is fundamentally limited to convey only one of three messages, or 1.58 bits. The new experiment surpasses that threshold by employing pairs of photons entangled in more ways than one (hyper-entangled). As a result, additional information can be sent and correctly decoded to achieve the full power of dense coding.

Kwiat, graduate student Julio Barreiro and postdoctoral researcher Tzu-Chieh Wei (now at the University of Waterloo) describe their recent experiment in a paper accepted for publication in the journal Nature Physics, and posted on its Web site.

Through the process of spontaneous parametric down conversion in a pair of nonlinear crystals, the researchers first produce pairs of photons simultaneously entangled in polarization, or “wiggling” direction, and in orbital angular momentum, or “twisting” direction. They then encode a message in the polarization state by applying birefringent phase shifts with a pair of liquid crystals.

“While hyper-entanglement in spin and orbital angular momentum enables the transmission of two bits with a single photon,” Barreiro said, “atmospheric turbulence can cause some of the quantum states to easily decohere, thus limiting their likely communication application to satellite-to-satellite transmissions.”

Editor’s note: To reach Paul Kwiat, call 217-333-9116; e-mail: kwiat@illinois.edu

Read Next

Health and medicine Dr. Timothy Fan, left, sits in a consulting room with the pet owner. Between them stands the dog, who is looking off toward Fan.

How are veterinarians advancing cancer research in dogs, people?

CHAMPAIGN, Ill. — People are beginning to realize that dogs share a lot more with humans than just their homes and habits. Some spontaneously occurring cancers in dogs are genetically very similar to those in people and respond to treatment in similar ways. This means inventive new treatments in dogs, when effective, may also be […]

Honors From left, individuals awarded the 2025 Campus Awards for Excellence in Public Engagement are Antoinette Burton, director of the Humanities Research Institute; Ariana Mizan, undergraduate student in strategy, innovation and entrepreneurship; Lee Ragsdale, the reentry resource program director for the Education Justice Project; and Ananya Yammanuru, a graduate student in computer science. Photos provided.

Awards recognize excellence in public engagement

The 2025 Campus Awards for Excellence in Public Engagement were recently awarded to faculty, staff and community members who address critical societal issues.

Uncategorized Portrait of the researchers standing outside in front of a grove of trees.

Study links influenza A viral infection to microbiome, brain gene expression changes

CHAMPAIGN, Ill. — In a study of newborn piglets, infection with influenza A was associated with disruptions in the piglets’ nasal and gut microbiomes and with potentially detrimental changes in gene activity in the hippocampus, a brain structure that plays a central role in learning and memory. Maternal vaccination against the virus during pregnancy appeared […]

Strategic Communications and Marketing News Bureau

507 E. Green St
MC-426
Champaign, IL 61820

Email: stratcom@illinois.edu

Phone (217) 333-5010