[qoqms-meetings] FW: Upcoming QCS Hub virtual seminars

[Andrew Daley]

From: Adi Sheward-Himpson <adi.sheward-himpson at physics.ox.ac.uk>
Sent: 18 September 2020 13:52
To: qcshub_all at maillist.ox.ac.uk
Subject: Upcoming QCS Hub virtual seminars

Dear all,

Following today’s fantastic talk from Ben Griffiths I’d like to let you know about next month’s QCS Hub seminars. As always these will be at 1.00pm on alternate Fridays and are as follows:

October 2nd

Quantum walks and electrical networks - Stephen Piddock

Finding a marked vertex in a graph is a classic computer science problem. One natural way to use a quantum computer to solve this problem is to design an algorithm based on a quantum random walk. If the walk starts in the stationary distribution of the graph, it is well known that the quantum walk provides a square root speedup over the corresponding classical random walk. In this talk Stephen will introduce the Szegedy quantum walk and describe how it can be analysed using the beautiful theory of effective resistance and electrical networks, which has proven to be a very productive tool in the study of classical random walks. This allows us to generalize the previous quantum walk results to the case where the walk starts in an arbitrary initial state, obtaining a run time that scales as the square root of the return time of the corresponding classical walk.

Stephen’s research has mainly focused on the computational complexity of features of the ground space of quantum Hamiltonians, and related questions concerning analogue Hamiltonian simulation. He is also interested in quantum algorithms, in particular quantum walks.

October 16th

High Coherence in a Tileable Superconducting Quantum Circuit – Peter Spring

Superconducting circuits are a promising platform for quantum computing. The largest devices now contain approximately 100 qubits. However, these devices do not naturally scale without suffering from wiring limitations and/or the emergence of spurious low-frequency modes. Here we present experimental results on a four-qubit device featuring 3D control wiring, flip-chip readout, and inductive shunting of the enclosure with a micro-machined pillar. We measure T1 times all greater than 100us, qubit-drive selectivities exceeding 50dB, and single qubit gate fidelities exceeding 99.9%. We then present simulations and theory for how the device attributes allow it to tile naturally to much larger 2D grids of qubits without suffering from wiring limitations or spurious low-frequency modes. These results indicate a promising architecture for surface code demonstrations with superconducting circuits.

Peter Spring is a fourth year DPhil student working with superconducting circuits in Peter Leek’s lab at the University of Oxford. His special interest is investigating solutions to scaling challenges in superconducting circuit hardware.

October 30th

Efficient Algorithms for Approximating Quantum Partition Functions – Ryan Mann

We establish a polynomial-time approximation algorithm for partition functions of quantum spin models at high temperature. Our algorithm is based on the quantum cluster expansion of Netočny and Redig and the cluster expansion approach to designing algorithms due to Helmuth, Perkins, and Regts. Similar results have previously been obtained by related methods, and our main contribution is a simple and slightly sharper analysis for the case of pairwise interactions on bounded-degree graphs. This is joint work with Tyler Helmuth.

Ryan is currently a postdoctoral research associate in the Quantum Information Theory group at the University of Bristol. His research interests are in quantum physics, complexity theory, and combinatorics. Recently, he has been using the relationship between quantum physics and combinatorial structures to answer problems arising in quantum algorithms and complexity.

We hope you’ll be able to join us for these seminars – put the dates in your calendars now!

Best wishes,

Adi

--

Adi Sheward-Himpson (Pronouns: he/him)
Communications Manager
QCS Hub – An EPSRC-funded project, part of the UKNQTP

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Department of Physics, Oxford University
Clarendon Laboratory, Parks Rd, Oxford OX1 3PU
Email: adi.sheward-himpson at physics.ox.ac.uk<mailto:adi.sheward-himpson at physics.ox.ac.uk>

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