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CREST HEP-QC seminar: PM14:00-, 24th Jun. (Tue) 2025

Title: Tensor renormalization group study of pure Yang-Mills theories in 2+1 dimensions

Speaker: Atis Yosprakob (YITP)

Abstract: We present a tensor renormalization group (TRG) simulation of pure SU(N) gauge theories in 2+1 dimensions for N=2 and N=3. The simulations are carried out on a dual lattice using the armillary sphere formalism, which analytically eliminates unphysical degrees of freedom in the lattice. The reduced model enables high-precision calculations compared to the original model at both zero and finite temperatures. In particular, we identify the deconfinement transition, consistent with those obtained from Monte Carlo simulations.

CREST HEP-QC seminar: AM10:00-, 12th May (Mon) 2025

Title: Critical behavior of the Schwinger model via gauge-invariant variational uniform matrix product states

Speaker: Kohei Fujikura (YITP)

Abstract: We study the lattice Schwinger model by combining the variational uniform matrix product state (VUMPS) algorithm with a gauge-invariant matrix product ansatz that locally enforces the Gauss law constraint. Both the continuum and lattice versions of the Schwinger model with θ=π are known to exhibit first-order phase transitions for the values of the fermion mass above a critical value, where a second-order phase transition occurs. Our algorithm enables a precise determination of the critical point in the continuum theory. We further analyze the scaling in the simultaneous critical and continuum limits and confirm that the data collapse aligns with the Ising universality class to remarkable precision.

CREST HEP-QC seminar: AM10:00-, 9th Apr. (Wed) 2025

Title: Z_N lattice gauge theory: toy model for quantum simulation

Speaker: Arata Yamamoto (University of Tokyo)

Abstract: In high energy physics, realistic gauge theory has continuous gauge symmetry such as U(1) and SU(N). Quantum simulation of continuous gauge theory is however difficult due to its infinite-dimensional Hilbert space. Discrete gauge theory is used for benchmarking near-term devices and algorithms. In this seminar, I will present the introduction of Z_N lattice gauge theory and its application to quantum simulation.

CREST HEP-QC seminar: AM10:00-, 19th Feb. (Wed) 2025

Title: Improving threshold and decoding for fault-tolerant color code quantum computing

Speaker: Yugo Takada (Osaka University)

Abstract: Color codes are promising quantum error-correcting codes because they have an advantage over surface codes in that all Clifford gates can be implemented transversally. However, they also have drawbacks: decoding is difficult, and the error threshold is low. In this seminar, I will talk about two works that address these drawbacks. In Ref. [1], an Ising model formulation for decoding is proposed, and numerical results demonstrate that a decoder using this formulation achieves high accuracy. Ref. [2] presents a method to improve the error threshold by optimizing decoder weights using flag qubits. In numerical simulations, we show that the threshold has been improved compared to previous studies.
[1] Y Takada, Y Takeuchi, and K Fujii, Phys. Rev. Research 6, 013092 (2024).
[2] Y Takada and K Fujii, PRX Quantum 5, 030352 (2024).
Slide(PDF file)