I am interested in exploring dynamical phenomena that occur in strongly interacting quantum many-body systems in out of equilibrium and designing their novel applications for quantum information science. This research topic is extremely rich and often involves a wide variety of interdisciplinary approaches to study: from analytic theory and numerical computations to experiments with controlled quantum degrees of freedom.
Below are brief descriptions of a few recent research topics:
Quantum Information Science
Dynamics of quantum information
Quantum information science seeks to understand and control quantum systems with high entanglement and complexity, defining a new frontier of physics. Recently, we have studied a novel phenomenon that arises in this regime: a phase transition in the dynamics of quantum entanglement and information. We consider a generic quantum many-body system coupled to a noisy environment, which we model with random unitary circuits interspersed by projective measurements. The interplay between unitary evolution and measurements leads to a phase transition: at high measurement rates, any coherent information in the system is completely lost, while at sufficiently low rates, an extensive amount of information is robustly protected. The nature of the phase transition can be understood from two complementary perspectives: firstly, by using the quantum error-correcting properties of scrambling unitary dynamics; and secondly, by using a mapping to ordering transitions in classical statistical mechanics.
Related works:
- Theory of the phase transition in random unitary circuits with measurements, Editor's suggestion (https://doi.org/10.1103/PhysRevB.101.10430)
- Quantum error correction in scrambling dynamics and measurement-induced phase transition (https://doi.org/10.1103/PhysRevLett.125.030505)
Quantum Convolutional Neural Networks
Neural network-based machine learning has recently proven successful for many complex applications ranging from image recognition to precision medicine. However, its direct application to problems in quantum physics is challenging due to the exponential complexity of many-body systems. Motivated by recent advances in realizing quantum information processors, we introduce and analyse a quantum circuit-based algorithm inspired by convolutional neural networks, a highly effective model in machine learning. Our quantum convolutional neural network (QCNN) uses only O(log(N)) variational parameters for input sizes of N qubits, allowing for its efficient training and implementation on realistic, near-term quantum devices. To explicitly illustrate its capabilities, we show that QCNNs can accurately recognize quantum states associated with a one-dimensional symmetry-protected topological phase, with performance surpassing existing approaches. We further demonstrate that QCNNs can be used to devise a quantum error correction scheme optimized for a given, unknown error model that substantially outperforms known quantum codes of comparable complexity. The potential experimental realizations and generalizations of QCNNs are also discussed.
Related works:
- Quantum convolutional neural networks (https://doi.org/10.1038/s41567-019-0648-8)
Control of quantum many-body Hamiltonian
One of the most outstanding challenges in the experimental study of quantum many-body dynamics is the difficulty of realizing systems with a desired Hamiltonian. Also, even if such a system is built, the "in vivo'' characterization of its Hamiltonian remains non-trivial. We study the theoretical tool sets to circumvent theses difficulties.
Related works:
- Dynamical engineering of interactions in qudit ensembles (http://arxiv.org/abs/1703.09808)
- Dynamically induced many-body localization (http://arxiv.org/abs/1703.03809)
Novel quantum applications of NV centers
A nitrogen-vacancy color center (NV center) in diamond possesses a lot of interesting and useful features. Consisting of a nitrogen substitute of a carbon atom and a nearby vacancy, a NV center traps an extra electron and behaves as an effective artificial atom. One of the most fascinating characteristics of it is that a NV center can be coherently manipulated, just like a trapped ultra cold atom, for long enough time, but now even at room temperature! We explore the potential applications of this quantum object in various contexts ranging from magnetometry to NMR imaging or to a novel experimental platform of studying many-body quantum dynamics.
Related works:
- Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit (http://dx.doi.org/10.1126/science.aaa4298)
- Nuclear magnetic resonance detection and spectroscopy of single proteins using quantum logic (http://dx.doi.org/10.1126/science.aad8022)
- Magnetic resonance spectroscopy of an atomically thin material using a single-spin qubit (http://dx.doi.org/10.1126/science.aal2538)
- Depolarization dynamics in a strongly interacting solid-state spin ensemble (http://dx.doi.org/10.1103/PhysRevLett.118.093601)
Nonequilbrium Quantum Many-Body Physics
Exotic phases of matter and quantum dynamics in strongly disordered systems
Under strong disorder, the coherent dynamics of a quantum system may be qualitatively different from that of a clean system. Recent developments of many-body localization suggest that the dynamics of such systems may be rather simpler than solving a full quantum problem and sometimes even controllable thanks to its localized nature. We study the nature of dynamics in such systems in both theory and experiments.
Related works:
- Quantum control of many-body localized states (http://arxiv.org/abs/1508.06992)
- Critical thermalization of a disordered dipolar spin system in diamond (http://arxiv.org/abs/1609.08216)
- Observation of discrete time-crystalline order in a disordered dipolar many-body system (http://dx.doi.org/10.1038/nature21426)
- Critical time crystals in dipolar systems (http://arxiv.org/abs/1703:04593)
Strongly interacting photons in Rydberg-EIT medium
A strong photon-photon interaction can be enabled via Rydberg-EIT mechanism. Already realized in experiments, such a system exhibits interesting quantum phenomena due to its unconventional form of the interaction. We study the dynamics of multiple photons with various types of interactions.
Related works:
- Scattering resonances and bound states for strongly interacting Rydberg polaritons (http://dx.doi.org/10.1103/PhysRevA.90.053804)
- Coulomb Bound States of Strongly Interacting Photons (http://dx.doi.org/10.1103/PhysRevLett.115.123601)
- Symmetry-protected collisions between strongly interacting photons (http://dx.doi.org/10.1038/nature20823)