QuICS seminar

Abstract: We discuss recent progress on entanglement catalysis, including the equivalence between catalytic and asymptotic transformations of quantum states and the impossibility to distill entanglement from states having positive partial transpose, even in the presence of a catalyst. A more general notion of catalysis is the concept of entanglement battery. In this framework, we show that a reversible manipulation of entangled states is possible.

Abstract: In this talk I will describe Decoded Quantum Interferometry (DQI), a quantum algorithm for reducing classical optimization problems to classical decoding problems by exploiting structure in the Fourier spectrum of the objective function. (See: https://arxiv.org/abs/2408.08292.) For a regression problem called optimal polynomial intersection, which has been previously studied in the contexts of coding theory and cryptanalysis, we believe DQI achieves an exponential quantum speedup.

Abstract: Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. I will discuss two approaches to better understand the role of quantum complexity in many-body physics. First, we'll consider random circuits, a model for chaotic dynamics. In such circuits, the quantum complexity grows linearly until it saturates at a value exponential in the system size.

Abstract: In this work we present fast constructions for the quantum Fourier transform and quantum integer multiplication, using few ancilla qubits compared to the size of the input. For the approximate QFT we achieve depth O(log n) using only n + O(n / log n) total qubits, by applying a new technique we call "optimistic quantum circuits." To our knowledge this is the first circuit for the AQFT with space-time product O(n log n), matching a known lower bound. For multiplication, we construct circuits that use no ancilla qubits and only O(n^(1+eps)) gates (for arbitrary eps>0).

Abstract: Light is quantum. Hence, quantifying and attaining fundamental limits of transmitting, processing and extracting information encoded in light must use quantum analyses. This talk is aimed at elucidating this using principles from information and estimation theories, and quantum modeling of light. We will discuss nuances of “informationally optimal” measurements on so-called Gaussian states of light in the contexts of a few different metrics.

Abstract: Quantum computing hardware capabilities have grown tremendously over the past decade, as evidenced by demonstrations of both quantum advantage and error-corrected logical qubits.  These breakthroughs have been driven, in part, by advances in quantum characterization, verification, and validation (QCVV).  I will discuss how QCVV provides a hardware-agnostic framework for assessing the performance of quantum computers; I will describe in detail how specific QCVV protocols (such as gate set tomography and robust phase estimation) have been used to characterize and sig

Abstract: The task of quantum position verification (QPV) deploys quantum information with the aim to use a party's position as a cryptographic credential. One well-studied proposed protocol for this task, f-routing, involves a mixture of classical information and a single quantum bit that has to be routed somewhere as a function of the classical information.

Abstract: I will review the concept of Floquet quantum error-correcting codes, and, more generally, dynamic codes. These codes are defined through sequences of low-weight measurements that change the instantaneous code in time and enable error correction.  I will explain a few viewpoints on these codes, including state teleportation and anyon condensation, and will explain how to implement gates purely by adjusting the sequences of low-weight measurement.

Abstract: The unification of quantum mechanics and gravity is a major outstanding goal. One modern approach to understanding this unification goes by the name ``holography’’, in which gravity can be understood as an emergent description of some more fundamental, purely quantum mechanical system. In this talk I will describe some recent results in holography that elucidate how this emergence works. A starring role will be played by one-shot quantum information theory.

Abstract: Noise on quantum devices is much more complex than it is commonly given credit. Far from usual models of decoherence, nearly all quantum devices are plagued both by a continuum of environments and temporal instabilities. These induce noisy quantum and classical correlations at the level of the circuit. The relevant spatiotemporal effects are difficult enough to understand, let alone combat. There is presently a lack of either scalable or complete methods to address the phenomena responsible for scrambling and loss of quantum information.