WQI News

Not so defective, after all: Demystifying advanced quantum materials

Sometimes, flaws are what makes a thing special.

That’s the case for a type of material called optical quantum emitters, which send out light in an exceptionally precise manner, one photon at a time, often due to tiny imperfections in a crystal’s structure.

The ability to emit light one photon at a time could allow optical quantum emitters to become the backbones of ultrafast computers, super high-resolution sensors and uncrackable long-range secure communication technologies.

Recently, buzz has been building about a newly discovered variety of quantum emitters consisting of two-dimensional materials (think flat sheets only as thick as a single molecule, similar to graphene). But there’s a hitch: No one truly understands the exact natures of the tiny flaws, called defects, that cause these two-di materials to become optical quantum emitters. And that’s been a major obstacle in obtaining these potentially useful materials.

This story continues on the College of Engineering’s site.

Measurement of a superconducting qubit with a microwave photon counter

 

The superconducting qubit group at WQI introduced an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92% [Science, 361, 1239 (2018)]. This scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface, see this article for broader perspective on this technology.

Read the full article at: http://science.sciencemag.org/content/361/6408/1239

Effects of charge noise on a pulse-gated singlet-triplet qubit

We study the dynamics of a pulse-gated semiconductor double quantum dot qubit. In our experiments, the qubit coherence times are relatively long, but the visibility of the quantum oscillations is low. We show that these observations are consistent with a theory that incorporates decoherence arising from charge noise that gives rise to detuning fluctuations of the double dot.

 

Read the full article at: https://arxiv.org/abs/1701.06971

Quasiparticle poisoning of superconducting microwave resonators

Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection.

Read the full article at: https://arxiv.org/abs/1610.09351