Exploring the origin of the Universe with nonclassicality of primordial gravitational waves

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K03827
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 15010:Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: Kyushu University (2020-2022); Osaka University (2019)
• Principal Investigator: Kanno Sugumi 九州大学, 理学研究院, 准教授 (70827427)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 原始重力波 / グラビトン / エンタングルメント

Outline of Final Research Achievements

We considered the possible detection of nonclassicality of primordial gravitational waves (PGWs) by applying Hanbury-Brown and Twiss (HBT) interferometry to cosmology. We characterized the nonclassicality of PGWs in terms of sub-Poissonian statistics that can be measured by the HBT interferometry. We showed that the presence of classical sources during inflation makes it possible to detect nonclassical PGWs with the HBT interferometry. It turned out that PGWs with frequencies higher than 10 kHz enable us to detect their nonclassicality.
As another method to detect the nonclassical PGW, we proposed an experiment that the entanglement between two macroscopic mirrors suspended at the end of an equal-arm interferometer is destroyed by the noise of gravitons through bremsstrahlung. We estimated that the decoherence time induced by the noise of gravitons in squeezed states stemming from inflation is approximately 20 seconds for 40 km long arms and 40 kg mirrors.

Free Research Field

宇宙論、重力理論

Academic Significance and Societal Importance of the Research Achievements

原始重力波の量子性をハンブリー・ブラウンとトゥイス干渉計を用いて、直接的に観測できる振動数領域を予言した。また原始重力波の量子であるグラビトンが、巨視的量子物体に対するノイズになることでデコヒーレンスを起こし、そのデコヒーレンス時間を測定することで、グラビトンを間接的に観測する方法を提案した。これらの観測方法が将来実現できれば、私たちの宇宙の起源が確かに量子揺らぎであったことが明らかになる。原始重力波の量子性の検出に成功すれば、未だに存在が確認されていないグラビトンの発見にもつながり、量子重力理論研究への波及効果が期待できる。