Our experiments at ultralow temperatures

This is the base plate of a dilution refrigerator that can bring our setup to about one-hundredth of a degree from the absolute zero so that we can perform our quantum physics experiments. Behind the microwave circuit is the mixing chamber (silver cylinder) that contains a mixture of helium-3 and -4 isotopes during the operation. Cooling to about 0.01 Kelvin is achieved by pumping the helium-3 from the concentrated to dilute phase of the mixture. Coppers are plated with gold to enhance the thermal conductivity which is dominated by the electronic heat diffusion at the ultra-low temperature.

Instrumentation strategies of QCD axion haloscope

Pleasure of Finding Things Out (together)

Graphene-based microwave bolometer

Electrons in graphene has extremely small heat capacity and thermal conductance because of its pseudo-relativistic band structure. It is a promising material for bolometry and single-photon calorimetry. This pseudo-colored image is the optical micrograph of the graphene bolometer that we invented, designed, fabricated, and studied. Detector physics is intimately related to fundamental questions of quantum measurements. In this case, our bolometer reaches the fundamental thermodynamic limit due to intrinsic fluctuation of temperature. Sensors with such a ultra-high sensitivity are very useful in creating remote entangled quantum states for quantum information and detecting the cosmic infrared background for radio-astronomy. This detector is scheduled to be deployed in the IBS's dark matter experiment in 2025.

Graphene-based single-photon detector

Kinetic inductance traveling wave amplifier (KIT)

This optical micrograph of KIT shows a roughly 2 meters long coplanar waveguide of about 1 micrometer wide, bending around to form the Yin-Yang pattern within a 10 by 10 mm2 footprint. It is micro-fabricated using niobium nitride by our collaborators in NIST and JPL, NASA. When properly biased and pumped, it can amplify a microwave signal by three-wave or four-wave mixing due to the non-linearity in the kinetic inductance of the superconductor. This amplifier can have a wide-band, high gain, and low noise amplification that will only be limited by the quantum principle. We uses KIT amplifier to simultaneously measure multiple qubits with high-fidelity.

Kinetic inductance and superfluid stiffness

Superconducting transmon qubit

Hydrodynamics of the Dirac fluid in graphene

This is an artistic rendering of the massless Dirac fermions exhibiting the hydrodynamic property because of the strong many-body interaction. We discover the experimental signature of the Dirac fluid by its violation of the Wiedemann-Franz law near the Dirac point, suggesting a non-Fermi liquid behavior. Theory predicts this is a nearly perfect fluid such that the viscosity-to-entropy ratio can approach the Kovtun-Son-Starinets bound. If graphene is disorder-free, the Dirac fluid is analogous to the quark-gluon plasma that forms in high energy collider and shortly after the Big Bang. This is a exemplary topic that we love to study in Quantum Wave-Matter group, showing how some big scientific ideas manifest in a table-top experiment!