Kin Chung Fong
Hydrodynamics physics in strongly correlated systems
Quantum materials: Graphene, Weyl, and topological materials
Quantum-sensing and quantum information technologies
Optical micrograph of a nano-fabricated, superconducting quantum bit (qubit).The qubit forms by a superconductor-insulator-superconductor Josephson junction (in the middle between the wire at the center that is barely visible) and a capacitor (the two big rectangles). It is capacitively coupled to other qubits or outside world via the superconducting microwave cavities (coplanar waveguides). This circuit-QED design is one of the basis of superconducting quantum information processing.
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.
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 calorimetry. We propose to detect a single light quanta using the graphene-based Josephson junction. 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.
Relativistic 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.
Kinetic inductance traveling wave amplifier (KIT). This image is taken under an optical microscope, showing a roughly 2 meters long coplanar waveguide of about 1 micrometer wide, bending around to form the Yin-Yang pattern. It is micro-fabricated using niobium nitride 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. The KIT amplifier can be used in high fidelity superconducting qubit measurements.
Magnetic Resonance Force Microscope that I designed and built for my Ph.D. thesis. The core of the microscope is a 90 micro-meter long cantilever that can detect magnetic resonance signal with sensitivity reaching a single electron magnetic moment. Reaching the record force detection sensitivity of 10-18N/Hz1/2 requires a shot-noise limited laser interferometry for cantilever displacement detection, scanning probe operation at cryogenic temperature, external and internal (3-springs pendulum in the picture) vibration isolation, and a magnetic field gradient up to 105 T/m. An important potential application of this microscope is to non-invasively image a macro-molecule by Magnetic Resonance Imaging (MRI) in atomic scale.
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