Title：Provably efficient machine learning for quantum many-body problems
Time：15:00-16:00pm, Nov 3 (Thur.) 2022
Abstract：Classical machine learning (ML) provides a potentially powerful approach to solving challenging quantum many-body problems in physics and chemistry. However, the advantages of ML over traditional methods have not been firmly established. In this talk, we will introduce a recent breakthrough in this area, which proves that classical ML algorithms can efficiently predict ground-state properties of gapped Hamiltonians after learning from other Hamiltonians in the same quantum phase of matter. By contrast, under a widely accepted conjecture, classical algorithms that do not learn from data cannot achieve the same guarantee. This talk is based on the work by Hsin-Yuan Huang, Richard Kueng, Giacomo Torlai, Victor V. Albert, and John Preskill.
Title：Shadow process tomography of quantum channels
Time：14:00-15:00pm, Oct 27 (Thur.) 2022
Abstract：Quantum process tomography is a critical capability for building quantum computers, enabling quantum networks, and understanding quantum sensors. Like quantum state tomography, the process tomography of an arbitrary quantum channel requires a number of measurements that scales exponentially in the number of qubits. However, the concept of shadow tomography has demonstrated the ability to extract key information about a quantum state with only polynomially many measurements. Recently, the idea of shadow tomography has been applied to characterize quantum processes. In this talk, we will introduce how this works. The talk is based on the work by Jonathan Kunjummen, Minh C. Tran, Daniel Carney, and Jacob M. Taylor.
Title：Constructing Smaller Pauli Twirling Sets for Arbitrary Error Channels
Speaker: Lijinzhi Lin（清华大学）
Time: 15:00-16:00pm, Oct 20 (Thur.) 2022
Venue: Ningzhai 宁斋S11
Abstract：Twirling is a technique widely used for converting arbitrary noise channels into Pauli channels in error threshold estimations of quantum error correction codes. Minimising the size of the twirling gate set increases the efficiency of simulations and in experiments it might reduce both the number of runs required and the circuit depth (and hence the error burden). Conventional twirling uses the full set of Pauli gates as the set of twirling gates. In this talk, we will introduce a theoretical background for Pauli twirling and a way to construct a twirling gate set with a number of members comparable to the size of the Pauli basis of the given error channel, which is usually much smaller than the full set of Pauli gates. The talk is based on the work by Zhenyu Cai and Simon C. Benjamin.
Title：Geometric approaches to quantum circuit complexity
Time：15:00-16:00pm, Oct 13 (Thur.) 2022
Abstract：Quantum computers hold great promise for solving interesting computational problems, but it remains a challenge to find the most efficient quantum circuits that can perform these complicated tasks. Particularly, what is the minimal size quantum circuit required to exactly implement a specified n-qubit unitary operation? It turns out that this fundamental problem can be reformulated as a geometric problem. In this talk, we will explain why this is possible.