Research
The Big Picture
Most practical phenomena, except those related to nuclear reactions, can be well described by atomic nuclei and electrons interacting with electromagnetic fields (photons) and gravity. The electromagnetic (EM) interaction becomes increasingly important at smaller length scales, and dominates in the meso- and microscopic world down to ~0.01 nm [figure adapted from Physics of Energy].
On the other hand, it is extremely difficult to solve the "simple" equations of motion for even a tiny piece of matter, especially condensed-phase matter (solids and liquids alike). For example, a 200-nm cube of silicon contains about 1 billion nuclei and ten billion electrons, all interacting electromagnetically. Therefore, we have been mostly studying Emergent Laws -- laws that govern new behaviors or patterns that emerge from a large collection of "simple" constituents (such as atoms, cells, or humans), at a particular length or energy (time) scale. A good example of emergent laws in condensed matter physics is the Fermi liquid theory.
To this end, although it is mostly the electrostatic component of EM interaction that holds condensed matter together, EM-matter interaction at higher frequencies (such as microwave, infrared, visible, and ultraviolet) excites all kinds of emergent degrees of freedom (such as free carriers, spins, phonons, and excitons) and is thus also extremely interesting and important. In fact, it is hard to spend a waking hour without using a piece of technology based on it (see above).
Our Scientific Interest
We are interested in electromagnetic-matter interaction in uncommon regimes. On the one hand, we develop new instruments that use microwave and light to probe the fundamental properties of quantum materials. On the other hand, we create new devices and structures that use unconventional materials and inverse design to generate, manipulate, and detect electromagnetic fields. Our research topics often lie at the interface between Microwave, Photonics and Quantum Materials. See below for a few examples, and also check out our Publications.
Current and near-term directions include (see also instrumentation section below):
Advanced microwave microscopy and spectroscopy
Broadband and nonlinear microwave impedance microscopy (MIM)
Correlated microwave and optical imaging of GHz electro/magneto/acoustic devices
Microwave photoconductivity nano-interferometry
Mid-infrared (MIR) photonics
Development of obstruction-free cryogenic MIR micro-spectrometer
Fluorescence of optical phonons
Dynamic BEC of micro-cavity optical phonon polaritons
Multi-physics inverse design
Expand adjoint-optimization-based inverse design to more physical realms
Intersection between Physics and AI
Physics-driven self-learning machines
Large language model analysis of physics literature and conference abstracts
Get in touch for more ideas.
Our Research Style
We are particularly focused on developing new instruments and protocols that provide unique insights. To achieve this, we create and combine a wide range of techniques that span the broad spectral range between microwave (GHz, μeV) and ultraviolet (PHz, ~10 eV), in the form of electronics, optics, and scanning probe microscopy. See a few examples below. With these new instruments, we collaborate extensively with our experimentalist colleagues who specialize in material growth, fabrication, or complementary techniques to carry out systematic experiments, and with our theorist colleagues to understand the data.
We like to leverage the immense industrial progress in computation, lithography, imaging, wireless communication, and photonics-based telecommunication whenever possible. For example, computational imaging has demonstrated amazing photography results with cheap optics and computation instead of expensive, bulky professional optics. Can we do something similar in solid-state optical microscopy or spectroscopy?
A cheap 3-axis digital magnetic field sensor controlled by a microcontroller is calibrated and placed in the middle of a PCB-based 3-axis orthogonal Helmholtz coil pairs. The currents in the Helmholtz coil pairs generate a vector magnetic field that cancels the earth's magnetic field (one div of the y axis in the real-time plot is 3 uT, or about 1/10 the earth field). This setup can readily sense the magnetic field from a steel ruler. The whole system costs ~$350 excluding the laptop, instead of >$20k for "professional" equipment of similar performance. Shot in Vuckovic lab @Stanford.
Along the same lines, we aspire to do Frugal Science and to DIY: combining creativity, maker's spirit, and high-volume components we can carry out unique experiments with a budget that is orders of magnitude lower than previously thought possible. From our experience, this approach deepens our understanding of the underlying physics, fosters problem-solving skills, and identifies what we need the most, which helps us make informed decisions even if we end up needing more specialized equipment. It also makes research more accessible (e.g. to undergrad students) and encourages more researchers to repeat our studies. Plus, it is just a lot more fun!
Our Broader Vision
Although most of our research is curiosity- instead of application-driven, we like to keep an eye out for potential applications in more applied fields, such as computation, sensing, imaging, displays, communications, and micro-manipulation. We are particularly interested in topics relevant to clean energy, beyond-von–Neumann computing, and human-computer interface (including extended reality). We always welcome collaborations from academia or industry.
The questions we like to contemplate include:
How can we make efficient nonlinear nodes for all-optical artificial neural networks (ANNs)?
Can we use anisotropic optical materials to make occlusion-capable displays for optical see-through augmented reality (AR)?
How do we make accurate, sensitive, and robust magnetic sensors with solid-state materials for brain-machine interface (BCI)?
Can we make non-invasive, long-lasting, and compact photonic sensors for real-time monitoring of important biochemical species in blood or extracellular fluid?
Can we use EM waves to manipulate the vestibular system to simulate the perception of motion and acceleration to make virtual reality (VR) much more immersive?
