May 2021 - ITP-quantumseminare - lists.phys.ethz.ch

Tomorrow's QIT Seminar
by Joe Renes 31 May '21

31 May '21

Hi all, Tomorrow we will hear from Sébastien Garmier on "The Shadow of a Rotating Black Hole". See below for the abstract. We start at 2pm on zoom: https://ethz.zoom.us/j/362994444 Best, Joe Abstract: The aim of this work is to provide an introduction to the field of shadows of rotating Kerr black holes. We review the mathematics of light propagation in Kerr spacetime and derive the equations describing the edge of a Kerr black hole shadow in the sky of a distant observer. We also discuss recent research concerning the possibility of determining the spin parameter a and the inclination angle $θ_O$ of the observer from direct observations of the shadow. Finally, we showcase two applications of the theory of black hole shadows to the Event Horizon Telescope collaboration image of the supermassive black hole M87*.

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Tomorrow's QIT Seminar
by Joe Renes 24 May '21

24 May '21

Hi all, Tomorrow we again have two speakers. Caroline Tornow will talk about "Improving Quantum Applications with Pulse-Level Compilation", and Clemens Giuliani will talk about "Variational Simulation of Quantum Circuits with Entangled-Plaquette States". See below for their abstracts. We'll start at 2pm on zoom: https://ethz.zoom.us/j/362994444 Best, Joe Speaker: Caroline Tornow Title: Improving Quantum Applications with Pulse-Level Compilation Abstract: The performance of near-term quantum algorithms, like the Quantum Approximate Optimization Algorithm, on state-of-the-art quantum computers is still significantly limited by noise. These algorithms are typically represented by quantum circuits in which unitary gates process the information. On the hardware level, these gates are implemented with calibrated control pulses. We demonstrate a novel pulse-efficient circuit transpilation methodology with Qiskit on IBM Quantum Computers, which scales cross-resonance entangling pulses to reduce the total duration of the quantum circuit in comparison to a Controlled-NOT (CNOT)-based quantum circuit. This procedure therefore makes a better usage of the finite qubit coherence time. By leveraging Cartan’s decomposition of SU(4) gates, we realize arbitrary pulse-scaled two-qubit gates and benchmark our technique on IBM Quantum devices using quantum process tomography. For almost all implementations we observe a significant error reduction of the pulse-efficient quantum gates in comparison to the respective CNOT gate-based implementations. As a sample application of the pulse-efficient methodology we implement circuits of a depth-one Quantum Approximate Optimization Algorithm applied to the Maximum Cut optimization problem for a non-hardware native 11-qubit graph. Here, we find that the circuit pulse duration is decreased by up to 52% and the error is reduced by up to 38%. Speaker: Clemens Giuliani Title: Variational Simulation of Quantum Circuits with Entangled-Plaquette States Abstract: While it is largely believed that the classical simulation of general large quantum circuits is hard to achieve it is often the case that specific quantum circuits can be approximated with classical variational algorithms. Variational representations used so far comprise tensor networks as well as neural network quantum states based on shallow architectures. In this work we introduce a simulation strategy for quantum circuits based on a different Ansatz called entangled- plaquette states (EPS), which have previously been used for simulating quantum systems on a lattice. Within this representation, we outline which classes of quantum gates can be applied exactly or approximately and give examples for both qubit and photonic quantum circuits. As an application we demonstrate that EPS can in principle be used to simulate the quantum approximate optimization algorithm. Furthermore we extend the previous variational fidelity optimization to wavefunctions which can be zero and present an implementation of the stochastic reconfiguration optimization algorithm with automatic differentiation.

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Tomorrow's QIT Seminar
by Joe Renes 17 May '21

17 May '21

Hi all, Tomorrow we begin the season of many master students finishing their thesis projects, in view of starting or applying to new positions in the fall. We will therefore have two talks in the seminar for the next few weeks. We kick it off with Nicola Quadri and Oriel Kiss, who both did their projects at IBM. See below for the titles and abstracts of their talks. We start at the usual time and "place", 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, Joe %%%%%%%%% *Speaker:* Nicola Quadri *Title:* Variational real-time evolution of U(1)-lattice gauge theories on digital quantum computers *Abstract: *Gauge theories are essential for describing the fundamental interactions between particles in the Standard Model. However, simulating real-time dynamics in gauge theories remains the most challenging task for classical computers, since the dimension of the Hilbert space grows exponentially with the system size. Quantum computers can offer a decisive alternative, as the quantum resources required to simulate an exponentially growing Hilbert space only increase polynomially. In this context, many hybrid quantum-classical algorithms—or variational quantum algorithms (VQAs)—have been developed in recent years to exploit the current noisy quantum hardware. One of the most promising algorithms in terms of simulating the real-time evolution of a quantum system is the variational time evolution (VTE), which may require significantly less quantum resources than the Trotterization method that is conventionally employed for quantum dynamics simulations. However, this poses the main problem of finding a variational ansatz that is able to describe the exact state along the entire evolution. We explore the VTE of abelian gauge theories, such as quantum electrodynamics (QED), for a (1+1)-spacetime dimensional lattice. We first discretize and encode continuous QED on qubits. Then, we compare the performance of the VTE using a physically motivated variational ansatz—used so far for stationary VQAs—with the Trotterization method for a growing system size. *Speaker: *Oriel Kiss *Title:* Quantum Neural Networks for electronic structure calculations *Abstract: *In a supervised learning setting, Quantum Neural Networks (QNNs) are quantum machine learning models described by the expectation value of some observable with respect to a quantum state expressed by a Parametrized Quantum Circuit (PQC). In this talk, we present a popular strategy to design this PQC, consisting of alternating encoding and variational layers, and apply this model to the computation of the potential energy surface and forces field for simple molecules. In chemistry applications, these can be used to drive molecular dynamics by integrating the equations of motion. We investigate the performances of our method in terms of accuracy and complexity, which are competitive with classical counterparts. In fact, QNNs can potentially achieve very high effective dimensions in model space, thus suggesting that they might be well suited to tackle complex learning tasks.

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Tomorrow's QIT Seminar
by Joe Renes 10 May '21

10 May '21

Hi all, Tomorrow we will hear from Fereshte Mozafari, who is visiting from EPFL and working with Yuxiang, on "Preparing uniform quantum states using Boolean methods". See below for the abstract. We start at 2pm on zoom: https://ethz.zoom.us/j/362994444 Best, Joe Abstract: A quantum algorithm to solve a specific problem is often described in terms of a quantum circuit and some quantum algorithms require a specific quantum state at the beginning of the computation. Therefore, efficient quantum state preparation is an important task. The preparation of quantum states is performed by a quantum circuit consisting of Controlled-NOT (CNOT) and single-qubit gates. Known algorithms to prepare arbitrary quantum states with n qubits create quantum circuits with O(2n) runtime and CNOTs that are relatively expensive over single-qubit gates in NISQ architectures. To reduce runtime and the number of CNOTs, we simplify the problem by only considering an important family of quantum states, which are Uniform Quantum States (UQSs). We map UQSs to Boolean functions and propose a Boolean method to prepare them. Our method simplifies the problem and enables us to apply well-understood techniques from logic synthesis.

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Tuesday's QIT Seminar
by Joe Renes 03 May '21

03 May '21

Hi all, This week Janek Denzler will tell us about his master thesis, entitled Semi-device-independent self-testing of unipartite systems based on contextuality. See below for the abstract. We start as usual at 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, Joe Abstract: Self-testing aims to characterize adversarial input-output devices from a minimal set of assumptions, by only interacting with the device classically. The vast majority of protocols rely on Bell non-locality and impose that the device be split into two non-communicating sub-devices. This talk will explore self-testing in a single verifier setting, where our device does not generate entanglement. This forces us to give up device-independence. We discuss the assumptions required by protocols based on the violation of non-contextuality inequalities, some of which are unphysical, and propose a new set of assumptions that facilitate robust self-testing of a unipartite system. Our protocol features a robust quantumness certificate, based on Spekkens contextuality.

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