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*.
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.
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.
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.
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.