# Online Seminar: Xun Gao (Harvard University), “Understanding the Linear Cross Entropy Benchmark through a Statistical Physics Model” #### calendar\_today Date and Time **May 11, 2021** 10:00AM - 10:00AM EDT #### pin\_drop Location **Zoom** **Location:** Zoom **Time:** Tuesday, May 11, 2021, 10:00 AM (Eastern US), 15:00 (UK/Eire), 16:00 (Central Europe), 22:00 (China) **Title:** Understanding the Linear Cross Entropy Benchmark through a Statistical Physics Model **Abstract:** In a recent experiment, Google claimed to achieve quantum advantage based on sampling from random quantum circuits. To certify the correctness of the sampling task, they developed a linear cross- entropy benchmark (XEB) and made their claim based on achieving a high value of XEB. The implicit assumption made in Google’s claim is that XEB approximates the fidelity well and hence could serve as a proxy in practice. However, it turns out that XEB can often deviate from fidelity, so it is crucial to understand how XEB and fidelity are related. I introduce a novel approach to analyze XEB through a mapping of random quantum circuits to a discrete classical statistical-physics diffusion-reaction model. By analyzing this model both qualitatively and numerically, we show that XEB usually overestimates fidelity These results indicate that one needs a new benchmark to certify quantum advantage. **Additional Ways to Join** Join by telephone (use any number to dial in) +1 929 436 2866 +1 312 626 6799 +1 669 900 6833 400 669 9381 China Toll-free International numbers available: [https://harvar](https://harvard.zoom.us/u/aclg6kOggb)[d.zoom.us/u/aclg6kOggb](https://harvard.zoom.us/u/aclg6kOggb) One tap mobile: +19294362866,,779283357# US (New York) Join by SIP conference room system Meeting ID: 779 283 357 <779283357@zoomcrc.com> --- Attachments- [ picture\_as\_pdf gao\_seminar\_may\_11\_2021.pdf ](/sites/g/files/omnuum6611/files/mathpicture/files/gao_seminar_may_11_2021.pdf) --- Share on:- [ Facebook ](#) - [ Twitter ](#) - [ Linkedin ](#) Save: [ Add to calendar calendar\_today ](https://mathpicture.fas.harvard.edu/node/1590338/event-feed.ics) Copy link link