ITP-quantumseminare

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This weeks QIT seminar
by Ladina Hausmann 26 Feb '24

26 Feb '24

Hi all, There is no QIT seminar planned for this week. Best, Ladina

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Thursday's weeks QIT seminar in HIT K 52 at 14:00
by Ladina Hausmann 19 Feb '24

19 Feb '24

Hi all, In this semester we the QIT seminar will be on Thursday’s at 14:00. This week our visitor Markus Frembs will talk about “Coming full circle? A cyclic perspective on Kochen-Specker contextuality”. See below for the abstract. This week the talk will be in HIT K 52. Best, Ladina *** Title: Coming full circle? A cyclic perspective on Kochen-Specker contextuality Abstract: Contextuality is a key distinguishing feature between classical and quantum physics. As a generalisation of nonlocality, it persistently fuels debates on quantum foundations. In turn, understood as a resource for quantum computation, it is expected to hold the key to quantum advantage. Yet, despite its long recognised importance in quantum foundations and, more recently, in quantum computation, the essence of contextuality remains elusive: many different mathematical frameworks exist, each addressing slightly different aspects of the phenomenon, yet leaving various questions open. In this talk, I will advocate a framework for contextuality, which subsumes various existing notions and approaches. Within this framework, I will motivate and introduce a conceptually new tool, which offers a fresh perspective on contextuality and captures its essence geometrically. I will then draw a number of consequences from this idea. In particular, I will resolve the apparent discrepancy between the original notion of contextuality, as introduced by Kochen and Specker, and the modern notion captured by noncontextuality inequalities.

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Tomorrows QIT seminar in H42 at 14:00
by Ladina Hausmann 12 Feb '24

12 Feb '24

Hi all, Tomorrow Moritz Scheer will tell us about his master thesis entitled "Quantum Advantage in Derivative Pricing & Variationally Trained Gaussian Loaders". See below for the abstract. The talk will take place at 2pm in HIT H42. Best, Ladina *** Title: Quantum Advantage in Derivative Pricing & Variationally Trained Gaussian Loaders Abstract: Loading of probability distributions is an important subroutine in many quantum algorithms, necessary for example for pricing derivatives in finance. This talk gives an introduction to derivative pricing and explains its working-principle using European call options and auto-callable options as examples. It shows how a quadratic quantum speedup can be achieved by accelerating classical Monte-Carlo methods using amplitude estimation. An important subroutine in derivative pricing is the loading of Gaussian probability distributions into the quantum computer. The second part of the talk introduces variationally trained Gaussian loaders and presents a successful implementation both with the real-amplitudes ansatz and the variational Hamiltonian ansatz under ideal conditions. It is shown that this implementation struggles when taking the effects of estimation noise into account.

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Tomorrow's QIT Seminar at 14:00pm in HIT E 41.1
by Ladina Hausmann 05 Feb '24

05 Feb '24

Hi all, Tomorrow our Jan Seyfried will tell us about his master thesis entitled "Towards efficient testing for zero conditional mutual information ". See below for the abstract. The talk will take place at 2pm in HIT E 41.1 Best, Ladina *** Title: Towards efficient testing for zero conditional mutual information Abstract: In quantum learning theory, we aim to extract specific information from a state ρ using measurements on samples of ρ. It is natural to ask what the most sample efficient way to do so is. In this project, we studied the problem of determining whether the conditional mutual information of a tripartite quantum state (or of a classical probability distribution) is either zero or above a certain threshold. This decision problem is interesting because states with zero conditional mutual information are known to have a special structure, which results in interesting properties such as perfect recoverability from the loss of a subsystem under certain constraints. Even classically, the sample complexity of this decision problem is not fully understood, both in terms of achievability and optimality. As part of our work, and as a step towards a sample-efficient quantum algorithm, we present two algorithms with similar sample complexity for the classical regime. Our approaches can serve as an example of how existing algorithms for more general learning tasks can be combined to solve new, more specialized problems. They are also a natural application of robustness bounds and continuity statements, which are of independent interest.

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No group seminar this week
by Ladina Hausmann 29 Jan '24

29 Jan '24

Hi all, there is no group seminar scheduled for this week. Best, Ladina

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Tomorrow's QIT Seminar at 14:00pm in HIT E 41.1
by Ladina Hausmann 22 Jan '24

22 Jan '24

Hi all, Tomorrow our visitor Shunji Tsuchiya will tell us about "Evolution of entanglement entropy in strongly correlated bosons in an optical lattice". See below for the abstract. The talk will take place at 2pm in HIT E 41.1 Best, Ladina *** Title: Evolution of entanglement entropy in strongly correlated bosons in an optical lattice Abstract: We investigate the time evolution of the second-order Rényi entropy (RE) for bosons in a one-dimensional optical lattice following a sudden quench of the hopping amplitude [1]. Specifically, we examine systems that are quenched into the strongly correlated Mott-insulating (MI) regime from the MI limit. In this regime, the low-energy excited states can be effectively described by fermionic quasiparticles known as doublons and holons. They are excited in entangled pairs through the quench dynamics. By developing an effective theory, we derive a relation between the RE and correlation functions associated with doublons and holons. This relation allows us to analytically calculate the RE and obtain a physical picture for the RE in terms of doublon holon pairs. We show that the RE is proportional to the population of doublon-holon pairs that span the boundary of the subsystem. Our quasiparticle picture introduces some remarkable features that are absent in previous studies on the dynamics of entanglement entropy in free-fermion models. It provides with valuable insights into the dynamics of entanglement entropy in strongly-correlated systems. [1] Phys. Rev. Research 5, 043102 (2023)

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Tomorrow's QIT Seminar at 14:00pm in HIT E 41.1
by Ladina Hausmann 15 Jan '24

15 Jan '24

Hi all, Tomorrow Caroline Tornow will tell us about her thesis "Error-mitigated circuit knitting with classical communication". See below for the abstract. The talk will take place at 2pm in HIT E 41.1 Best, Ladina *** Title: Error-mitigated circuit knitting with classical communication Abstract: Large-scale fault-tolerant quantum computers are still out of reach. Furthermore, it is a key challenge to develop error mitigation methods for noisy quantum devices and run applications on the limited number of qubits. Circuit knitting allows the simulation of a quantum computer with more qubits than are physically available, however, at the expense of a simulation overhead. Here, a large quantum circuit is partitioned into multiple fragments that fit on devices with fewer qubits. In this work, we study a variant of this technique, called circuit knitting with classical communication [1] which employs classical communication between the circuit fragments. Naturally, circuit knitting with classical communication requires measurements which are carried out mid-circuit and, based on their outcomes, trigger quantum operations. Due to inevitable qubit idling times, these dynamic quantum circuits are currently more prone to noise than quantum circuits consisting only of unitary gates. The dominant noise sources are dephasing and quantum crosstalk. In this talk, we introduce circuit knitting with classical communication and its implementation on a noisy quantum computer. We present two techniques to suppress and mitigate noise, dynamical decoupling and zero-noise extrapolation, and show how they can be tailored to dynamic quantum circuits. Using these techniques, we demonstrate error-mitigated circuit knitting with classical communication for graph-state circuits. Our results indicate that error suppression and mitigation make quantum applications involving dynamic quantum circuits, such as circuit knitting, feasible on currently available noisy quantum computers. [1] C. Piveteau and D. Sutter, “Circuit knitting with classical communication”, IEEE Transactions on Information Theory (2023)

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Todays QIT Seminar at 2pm in HIT E41.1
by Ladina Hausmann 09 Jan '24

09 Jan '24

Hi all, I hope you had a good start in the new year! We are starting again this week with a talk from our guest Vojtěch Havlíček on “On Quantum Statistical Query Learning”. See below for the abstract. The talk will take place at 14:00 in HIT E41.1. Best, Ladina %%%%% Title: On Quantum Statistical Query Learning Joint work with Louis Schatzki (UIUC) and Srinivasan Arunachalam (IBM Almaden). Abstract: Statistical Query Learning (SQ) is a restriction of PAC learning in which learners form hypotheses by querying expectation values over the data distribution and labels. It is well known that SQ cannot learn the concept class of parities, even under uniform distribution. This shows that it is a restriction of PAC.   We study an obvious quantum generalization of SQ, proposed by Arunachalam, Grilo and Yuen, which is not separable from a quantum generalization of PAC by parity learning and our main result is a task that separates the two learning classes. To prove it, we built on Feldman‘s work on statistical query dimension, which yields lower bounds on SQ learning. I will discuss our result, the lower bounding technique and some of its applications.

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Tomorrow's QIT Seminar at 14:00pm in HIT E 41.1
by Ladina Hausmann 18 Dec '23

18 Dec '23

Hi all, Tomorrow Liuhang Ye will tell us about his thesis "Towards Understanding Quantum Causal Structures in Quantum Spacetimes". See below for the abstract. The talk will take place at 2pm in HIT E 41.1 Best, Ladina *** Title: Towards Understanding Quantum Causal Structures in Quantum Spacetimes Abstract: In general relativity, causality is deterministically governed by Einstein’s field equations. When matter is subjected to quantum mechanics, the anticipation arises that spacetime itself adopts a quantum nature, giving rise to novel causal structures. In this thesis, we compare different notions of causality and explore causal structures in the context of a specific information processing protocol — the quantum switch. We propose an operational definition of events that is applicable in beyond-classical-spacetime scenarios. Finally, we present two propositions concerning the fine-graining of the quantum switch in classical spacetimes and quantum spacetimes, respectively.

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Tomorrow's QIT Seminar at 14:00pm in HIT E 41.1
by Ladina Hausmann 11 Dec '23

11 Dec '23

Hi all, Tomorrow Valette Orane will tell us about their master thesis "Exploring the viability of cellular automaton decoders for the surface code". See below for the abstract. The talk will take place at 2pm in HIT E 41.1 Best, Ladina *** Title: Exploring the viability of cellular automaton decoders for the surface code Abstract: Quantum error correction has become indispensable in ensuring the protection of quantum information from noise and enabling fault-tolerant quantum computing. The Surface code is a quantum error-correcting code designed such that error-corrected qubits can be built in a two-dimensional architecture and only requiring local connectivity. Together with its high tolerance to quantum noise, the Surface Code currently stands as the most promising candidate for implementing error correction in quantum computing devices. In any error-correcting scheme, an integral component of the process is the decoding algorithms. They are tasked with producing accurate estimates of the errors from measured syndrome data so that these errors can subsequently be corrected. Such decoding algorithms need to be very fast but this speed requirement introduces a challenging tradeoff, where the complexity is only improved at the expense of accuracy and vice-versa. Interesting contestants for fast decoders are cellular automaton decoders. Because of their simplicity and how they reduce the decoding problem to simple local update rules, they exhibit reduced complexity. This reduced complexity however comes at the price of an accuracy that is lower than more complex algorithms, especially for codes like Surface codes without periodic boundaries. In this thesis, by building on previous projects of the group, we aim to investigate the viability of the cellular automaton decoder for the Surface Code, by experimenting with different ways of optimizing the algorithm for the Surface code with boundaries.

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ITP-quantumseminare