Study of quantum systems built inside a solid state of matter
Nanoscale photonic structures for applications in quantum computation, communication, and sensing
Quantum Nanophotonics studies light-matter interaction in systems with typical size below the diffraction limit. Examples of such systems include nanoscale plasmonic resonators, waveguides, metamaterials and metasurfaces coupled to single-photon emitters such as color centers or quantum dots. In these systems, the interaction between photons and emitters can be much stronger than in a homogenous environment, leading to a number of phenomena such as spontaneous lifetime reduction and coherent quantum dynamics that could lead to controlled entanglement of several emitters. The richness of near-field phenomena allows to further expand the engineering of light-matter interaction, by achieving high plasmon emission directionality and control of polarization. In addition, because the increase in interaction is due to small mode volumes rather than strong resonances, these effects can be rather broadband and apply to a great variety of emitters.
Driven by the applications of quantum control of light and matter, our group is developing efficient room-temperature compact on-chip configurations of quantum systems coupled to nanophotonic structures. Building on our expertise in the field of metamaterials and nanophotonics, we conceive new tunable CMOS-compatible materials and practical designs that will lead to a new generation of single-photon sources, quantum registers, detectors and quantum frequency converters for quantum communication, quantum computation and sensing.
The Greene group studies a wide variety of physical phenomena using primarily methods from theoretical atomic, molecular, and optical physics. The phenomena treated range from low energy few-body processes to many-body atomic, molecular and condensed matter systems using a diverse set of theoretical techniques. In the few-body regime, our group examines the behavior of neutral atoms under the influence of radio frequency light or synthetic gauge fields, in addition to conventional electron or photon collision phenomena from low energies up to the X-ray regime. This area also includes studies of highly excited Rydberg atoms interacting with external fields or other neutral atoms. Additional explorations in the few--body regime tackle fundamentally challenging problems involving cold chemistry and the photoassociation of atoms and ions. A recent direction is an extension of our few-body techniques into the realm of many-body physics in a treatment of the two-dimensional quantum Hall system. While the variety of topics considered is far-ranging, all of these studies are connected by the fact that these are quantum mechanical systems with nonperturbative interactions that are highly challenging for existing theoretical methods.
His research focuses on improving the performance of photovoltaic, thermophotovoltaic, and nonlinear systems using the principles of nanophotonics. Key enabling techniques for his work include electromagnetic and electronic theory, modeling, simulation, fabrication, and characterization.
MEMS-mediated spin entanglement in silicon carbide. Silicon carbide has di-vacancy defects that can simultaneously couple to microwave and optical field. We are working on mechanical resonances in silicon carbide to boost the inter-modal coupling and mediate entanglement between spin states and electromagnetic fields. Our group focuses on designing MEMS and ultrasonic resonators that can generate stress-waves which will interact and affect the spin-state of a defect, “shaking” them into spin-resonance. This project is a collaboration with Professor David Awschalom’s group at IME, University of Chicago.
Precision measurement of weak transitions in atomic systems provides insights into high-order interactions within the atom. The weak force, for example, one of the four fundamental forces of nature, can cause optical transitions in atoms that would not otherwise be permitted, to proceed. These transition rates, of course, are extremely small, and only the most sensitive of detection schemes can be used to measure them. Thus, atomic physics laboratory with table-top instruments can generate complementary measurements to those performed at high-energy accelerator laboratories. Detecting signals from such transitions requires high noise control and long data collection time. Examples of these weak transitions include magnetic dipole transitions, electric quadrupole transitions and parity non-conserving (PNC) transitions. Measurement of PNC transitions, in particular, is a direct probe of the weak interaction between the nucleons and the electrons. Experimentally measured PNC transitions would lead to a determination of the weak force and the weak charge, of as well as the anapole moment of the nucleus. These experimental results may further our understanding of fundamental physics and give rise to new physics beyond the standard model.
In addition, our lab focuses on creation and control of bi-alkali polar molecules, Li-Rb to be specific. Unlike naturally existing neutral and ionized molecules, these polar molecules tend to have strong dipole-dipole interaction and have a great potential for precision measurement, quantum computing and quantum simulation. The alkali metal atoms, lithium and rubidium, are cooled down to sub-milliKelvin temperatures in a magneto-optical trap (MOT), and made to combine into molecules using laser light through a process known as photoassociation. Amongst all other bi-alkali molecules, Li-Rb is a good candidate in that it has a high PA rate, and a strong dipole-dipole interaction.
Strong and coherent interaction of photons with matter is the corner stone of the future quantum optical technologies. Engineering coherent and efficient light-matter interactions at the single photon level using chip-scale devices is the grand challenge of the quantum photonic technology. Interaction of that kind enables new and exciting applications including secure optical communication, photonic quantum computing and quantum sensing.
In our group we are interested in studying strong quantum interaction of light with real and artificial atoms and its role in quantum optical communication, computation and sensing. We work towards developing a hybrid and scalable photonic network that operates at the telecommunication wavelength.
We are interested in using tabletop atomic, molecular and optical (AMO) systems to engineer novel quantum materials and study intriguing phenomena discussed across disciplines, from condensed matter to cosmology. To address topics over such a wide range, we exploit physics governed by universality, with which a cold cloud of dilute gases, for example, can behave similarly as an exotic quantum material in solid states, or even as a cosmic fluid in the early universe. AMO systems allow us to apply quantum control and measurements with great precision, offering a clean designer platform to explore fundamental issues in quantum mechanics, field theory, and statistical physics.
Our group’s research focusses broadly at the interface of quantum photonics, quantum materials and nanotechnology. We are involved in both theory and experiment while simultaneously collaborating with a broad range of faculty at Purdue and around the world. One recurring theme in our research is the study of thermal and quantum noise inside materials and their consequences on dipole-dipole interactions, vacuum forces and single photons.
In the early twentieth century, the new field of “quantum chemistry” was formed by the interaction of chemists, physicists, applied mathematicians and computer scientists. Our aim is to further catalyze and advance this field by building on discoveries at the nexus between modern theoretical chemistry and the new ideas emerging from quantum information theory and its foundations in quantum physics and computer science.
Enhancing interactions of light with matters, in particular biological and natural media is the essence of numerous research disciples including bioimaging and biosensing. We are interested in realizing biogenic light localization in the same manner of Nobel Prize winner Philip W. Anderson’s theory (also known as Anderson localization). Counterintuitively, partially irregular nanostructures, compared with perfectly ordered nanostructures, can provide unique advantages of enhanced light confinement, transport, and amplification, if light in such media is localized or confined spatially. We have identified several biological and natural nanomaterials for scalable and wearable integrations toward biomedical applications. By coupling single quantum dots into biogenic localized states, we expect to open a new possibility for cavity quantum electrodynamics taking advantage of natural irregularity in biological and natural media. Such hybridization will allow us to develop a new class of biosensors in which localized modes or resonances are extremely sensitive to subtle nanoscale perturbations.
Solid-state quantum computers based on quantum dots and dopants in semiconductors such as silicon offer the promise of scalability and long coherence times. However, the design and implementation of robust semiconductor qubits are challenging due to the complexity of the solid-state environment. Details of band degeneracies, atomic scale disorder, electrostatic potential, device geometry, electron-phonon interactions, many-particle effects, and spin-spin interactions, and time-dependence need to be captured in theoretical models to understand measurements of state-of-the-art experiments and to provide device design guidance. The conventional electrostatic modeling tools (TCAD) that are used for transistor modeling are not sufficient in this regime of electronics. Our group has developed a software tool called NEMO (Nano-Electronic Modeling) that aims to serve as a device design tool in this new regime of electronics. NEMO represents the single and multi-particle Schrodinger equation on an atomic orbital basis taking into account all the above-mentioned interactions.
Our group collaborates closely with several leading experimental groups in silicon quantum computing to interpret experiments, propose new designs, and to engineer robust solid-state qubits. Among various other experiments, NEMO has been used to model single-atom-transistors[1-2], spin blockade in double quantum dots, spin relaxation in few-electron quantum dots[4-6], exchange coupling in two-qubit gates, transport in atomic-scale nanowires, and STM imaging of dopant states. The tool has recently been extended to model III-V heterostructures for topological qubits and also to model optically addressed dopant qubits in silicon.
Recently developments in quantum optomechanics provide new opportunities to study macroscopic quantum mechanics and create ultrasensitive detectors. Creating large quantum superposition states (Schrödinger’s cat) with massive objects is one of the most challenging goals in macroscopic quantum mechanics. We have optically levitated nanodiamonds with nitrogen-vacancy (NV) centers in vacuum. We plan to generate large spatial superposition states and arbitrary phonon Fock states of levitated nanodiamonds using the NV spin-optomechanical coupling with the assistance of a strong magnetic field gradient. The large spatial superposition states can be used to study objective collapse theories of quantum mechanics. A levitated nano-optomechancial system will also be a sensitive force detector.
We are also interested in studying novel macroscopic quantum behaviors. Recently, we proposed a straightforward method to create quantum superposition states of a living microorganism by putting a small cryopreserved bacterium on top of an electromechanical oscillator. The internal states of a microorganism, such as the electron spin of a glycine radical, can also be entangled with its center-of-mass motion and teleported to a remote microorganism.
My research area is Theoretical Atomic Physics, mainly focusing on time dependent atomic phenomena, highly excited (Rydberg) atoms, electron scattering, strong fields and ultracold plasmas. My research group typically consists of undergrads, grad students and postdocs. I'm a member of the ALPHA collaboration which was the first group to trap the antimatter version of the Hydrogen atom and the first group to quantitatively measure some of its properties.
The Wasserman group works on the development of Density Functional Theory (DFT) for both ground-state and time-dependent quantum chemistry. In particular, Partition Density Functional Theory (PDFT) is a formally exact method for calculating the energy and density of electronic systems via self-consistent calculations on isolated fragments. PDFT allows for an accurate and efficient solution of the many-electron Schrodinger equation for complex molecules and materials, physically-motivated approximations are needed to calculate the partition potentials that enter the theory. Much of our research effort goes into developing and testing such approximations.
Entangled photons exhibit correlations that are unattainable with classical light. Their stronger-than-classical correlations make them desirable in applications ranging from secure communications to high-speed computation. Although, many degrees of freedom for entanglement exist, our research focuses on developing novel techniques for controlling time-frequency entangled photons (“biphotons”) that would be applicable in quantum communication. Most of our manipulation schemes have utilized broadband biphotons generated from spontaneous parametric down-conversion in periodically poled lithium niobate waveguides. However, we are also now exploring photon pair generation using silicon nitride microring resonators, a platform that could lead us to on-chip time-frequency manipulations.
Quantum nanophotonics with color centers in diamond »
Scalable Wearable Systems for Plasmonics and Photocatalysis »
Exploring many-body physics with strong atom-light interactions »
Rydberg physics »
Transparent sub-diffraction photonics »
Nano-Electronic Modeling »
Dipole-dipole interaction between atoms »
Ultra-cold LiRb molecules »
Shaping of Entangled Photons »
Quantum spin-optomechanics of levitated nanodiamonds »
Measurement of anapole moment of atomic cesium via two-pathway coherent control »
Measurement of parity non-conserving transitions in cesium via two-pathway coherent control »
Scalable Quantum Optical Network at the Telecommunication Wavelength »