Seminar

The search for exotic quantum phases of matter is a central theme in condensed matter physics. The advent of programmable quantum hardware provides an unprecedented access to novel quantum states and represents a new avenue for probing the exotic properties associated with topological order.. In this talk, I will discuss our progress in realization of topologically ordered ground states based on exact efficient quantum circuit representations.

Qubit-based noise spectroscopy (QNS) techniques, where the dephasing of a probe qubit is exploited to study a system of interest, underlie some of the most common quantum sensing and noise characterization protocols. They have a variety of applications, ranging from designing effective quantum control protocols to investigating properties (phase transitions, thermodynamics, etc.) of quantum many-body systems.

The two most prevalent classes of ordered states in quantum materials are those arising from spontaneous symmetry breaking (SSB) and from topological order. However, a systematic study for their coexistence in interacting systems is still lacking. In this talk, I will discuss how the topological configuration in order parameter spaces from SSB (classical topology) interplays with the symmetry protected/enriched topological orders (quantum topology) in two spatial dimensions (2d). Three examples of such systems will be given.

A central goal in quantum error correction is to reduce the overhead of fault-tolerant quantum computing by increasing noise thresholds and reducing the number of physical qubits required to sustain a logical qubit.

Many organized efforts across the world are racing to realize the "Quantum Internet" -- the internet of the future that is upgraded to provide an additional service: that of reliably transmitting qubits between distant users. Just like the internet's classical data communications service, the quantum communications service must reliably support many user groups, and support diverse and dynamic applications---each with its unique requirements on the quality of service for transmission of qubits, e.g., rate, latency, fidelity etc.

I will talk about:
. New efficient algorithms for quantum state tomography (the quantum analogue of estimating a probability distribution).
. Why you should care about the difference between total variation distance and Hellinger distance and KL divergence and chi-squared divergence.
. Quantum-inspired improvements to the classical problem of independence testing.

Includes joint work with Steven T. Flammia (Amazon)

ATL 3100A and Virtual Via Zoom.

At the heart of modern quantum technologies is the interference in the radiation of quantum emitters mediated by common vacuum modes. When there are many atoms interfering in the emission process, one observes enhancement or suppression of decay rate coefficient, which is called superradiance and subradiance, respectively [1]. When there are transitions from different excited levels interfering in the emission process, the intensity of the emitted light is modulated at the frequency of the excited level splittings, which is called quantum beats.

In the last few years, a number of works have proposed and improved provably efficient algorithms for learning the Hamiltonian from real-time dynamics. In this talk, I will first provide an overview of these developments, and then discuss how the Heisenberg limit, the fundamental precision limit imposed by quantum mechanics, can be reached for this task. I will show that reaching the Heisenberg limit requires techniques that are fundamentally different from previous ones.

Thermodynamics plays an important role both in the foundations of physics and in technological applications. An operational perspective adopted in recent years is to formulate it as a quantum resource theory. I will begin with a quick introduction to the general framework of quantum resource theories, in particular motivating it and explaining why the convertibility of resourceful states is at its core.