Institute of Computer Science AGH and IBM Software Laboratory in Krakow invite to Krakow Quantum Informatics Seminar (KQIS)**Objectives**:

• understand and discuss current problems in quantum informatics,

• discuss new quantum computing technologies,

• exchange ideas and research results,

• integrate information across different research teams,

• build a community around quantum informatics.**Venue**: via Internet, Webex https://ibm.webex.com/meet/tomasz.stopa**Program**:

Tuesday, 30th of March 2021, 9:30-11:00

**Oliver Reardon-Smith, **Jagiellonian University Quantum Resources Group

**Topic: Fast estimation of outcome probabilities for quantum circuits**

**Presentation **

**Abstract:**

We present classical algorithms for the simulation of universal quantum circuits on n qubits constructed from c instances of Clifford gates and t arbitrary-angle Z-rotation gates such as T gates. Our algorithms complement each other by performing best in different parameter regimes. The Estimate algorithm produces an additive precision estimate of the Born rule probability of a chosen measurement outcome with the only source of run-time inefficiency being a linear dependence on the stabilizer extent (which scales like ≈1.17t for T gates). Our algorithm is state-of-the-art for this task: as an example, in approximately 25 hours (on a standard desktop computer), we estimated the Born rule probability to within an additive error of 0.03, for a 50 qubit, 60 non-Clifford gate quantum circuit with more than 2000 Clifford gates. The Compute algorithm calculates the probability of a chosen measurement outcome to machine precision with run-time O(2t−r(t−r)t) where r is an efficiently computable, circuit-specific quantity. With high probability, r is very close to min{t,n−w} for random circuits with many Clifford gates, where w is the number of measured qubits. Compute can be effective in surprisingly challenging parameter regimes, e.g., we can randomly sample Clifford+T circuits with n=55, w=5, c=105 and t=80 T-gates, and then compute the Born rule probability with a run-time consistently less than 104 seconds using a single core of a standard desktop computer

**References:**

[1] Hakop Pashayan, Oliver Reardon-Smith, Kamil Korzekwa, Stephen D. Bartlett: Fast estimation of outcome probabilities for quantum circuits, arXiv:2101.12223 [quant-ph]

**Bio:** Oliver Reardon-Smith is a post-doc working in the group of Kamil Korzekwa, focusing on applying the framework of quantum resources to simulations and computational problems. He obtained his PhD from a maths department so he is also interested in a variety of theoretical and mathematical problems.