Scientific publications

The Institute for Quantum Computing (IQC) researchers continue to collaborate and publish their research with the top journals around the world.

The IQC Publications database provides access to scientific literature that has been authored or co-authored by IQC researchers.

Scientific highlights

IQC faculty, postdoctoral fellows and students continue to conduct internationally recognized quantum information science research. Here is a sampling of their cutting-edge research published in academic journals over the past term. 

Violating Bell's inequality with nanoscale light scources

Scientific Reports 7, 1700 (2017)

MICHAEL REIMER was part of an international team that achieved the first violation of Bell’s inequality in a photonic nanostructure with enhanced light extraction efficiency.

Researchers embedded highly symmetrical quantum dots – nano-sized artificial atoms that emit light – inside special nanowire structures theoretically able to create highly entangled photons with near-unity efficiency. Though the researchers did not yet reach this theoretical upper limit, they generated two orders of magnitude more entangled photon pairs than previously reported from standard quantum dot structures and conclusively violated Bell’s inequality.

Entangled photon pairs primarily have applicability in quantum communications and cryptography, which use the property of entanglement – where particles are so strongly linked that one cannot describe either of them individually – to generate unbreakable encryption keys. Achieving this entanglement means that photons show strong correlations in a way that cannot be explained by hidden, local relationships; this is quantified by violating Bell’s inequalities.

The high fidelities of photon entanglement achieved through this method stand to both increase the security of quantum cryptography and drastically reduce the time needed to complete quantum optics experiments.

The paper, Bright nanoscale source of deterministic entangled photon pairs violating Bell’s inequality, was published in Scientific Reports on May 10.

New causal structures only found in the quantum world

Nature Communications 8, 15149 (2017)

Building on past research which showed that in the quantum world, certain kinds of correlations do imply causation, a team of IQC researchers discovered that there are types of causal structures unique to the quantum realm.

The research team, which included IQC faculty member KEVIN RESCH and PhD student JEAN-PHILIPPE MacLEAN, found a kind of physical mixture of causal mechanisms that act quantumcoherently with one another.

The rich new possibilities implied by this discovery could lead to new insights into understanding the relationship between causality and quantum correlations, especially relating to entanglement. Causality is a fundamental concept for those in the fields of epidemiology, genetics and social sciences, and the research sheds new light to causal relationships in a quantum world.

The paper, Quantum-coherent mixtures of causal relations, was published in Nature Communications on May 9.

Study proves viability of quantum satellite communications

2017 Quantum Sci. Technol. 2 024009

After nearly eight years of preparation, IQC’s Quantum Encryption and Science Satellite (QEYSSat) team led by THOMAS JENNEWEIN achieved the first demonstration of quantum key distribution (QKD) from a ground transmitter to a quantum payload circling in an aircraft overhead.

The payload was designed to conform to the size and operating restrictions of a micro-satellite, ensuring that the test was a valid proof-of-concept demonstrating the viability of the QEYSSat prototype for future satellite missions.

Currently, ground-based QKD systems rely on optical fibers limited to distances of only a few hundred kilometers. Use of satellite systems stand to expand this distance to a global scale, allowing unbreakable quantum key encryption and communication around the world.

Experiment finds way to increase photon efficiency for quantum communications

Phys. Rev. Applied 8, 054015 (2017)

A team of IQC researchers demonstrated a new type of on-demand single photon generator that can shape photons to increase their efficiency when used in a quantum network.

“Our results show an important proofof-principle of an enabling technology for quantum networks, which is easily extensible to other types of physical systems beyond superconductors,” said faculty member CHRISTOPHER WILSON, principal investigator of the Engineered Quantum Systems Laboratory (EQSL). Former postdoctoral fellow POL-FORN DÍAZ, former master’s student CHRISTOPHER WARREN and PhD students CHUNG WAI SANDBO CHANG and VADIRAJ ANANTHAPADMANABHA RAO also contributed.

The new photon generator is a superconducting circuit comprised of two main parts. The first, a superconducting qubit, acts like an artificial atom that emits microwave light. The second is a superconducting transmission line that carries electrical signals through the circuit.

The ability to produce shaped photons is important for efficient absorption of photon pulses by distant nodes of a quantum network,” said Wilson. “This work further demonstrates how quantum microwaves are a resource for future quantum communication networks.”