How can one figure out how well a quantum computer works and what its dominant errors are?
We develop tomography, randomized benchmarking, gate set tomography and shadow estimation methods that extract reliable information about real hardware from as few experiments as possible -- and we prove when they can be trusted.

Running a quantum algorithm is not free: the answer has to be read out, often very often to gather statistics and to feature outer classical optimization loops. 
We design estimation strategies for chemistry and materials problems that reduce the number of measurements by orders of magnitude, and we analyze the true cost of variational approaches.

An algorithm written in gates must become a sequence of physical pulses.
We construct time-optimal multi-qubit gates, robust Hamiltonian engineering schemes and compilation methods that shorten circuits -- the most direct way to get more computation out of a device before it decoheres.

How far do classical solvers reach, and what can algorithms borrowed from quantum theory add?

1. We investigate state-of-the-art QUBO solvers (Ising machines), benchmark against strong classical baselines, and identify potential relevant problems that can be recast as QUBO problems.
2. We identify application areas for tensor-network methods in solving differential equations.

Fault-tolerant quantum computing requires knowing the noise you are correcting.
We develop statistically sound methods to learn error models directly from syndrome measurements, data that a running quantum computer produces anyway.

You cannot claim a quantum advantage without knowing what classical computers can do.
We study tensor networks, matrix product states and operators, locality of temperature and dissipative dynamics -- establishing the classical yardstick against which every advantage claim must be measured.

Some of the most useful results are negative ones.
We prove hardness and no-go theorems that identify limitations of popular approaches, so that effort goes where it can succeed.

We run a weekly group seminar on quantum computing and quantum information theory.
Guests are welcome; please contact us in advance.

• Publications
• All arXiv preprints by Martin Kliesch