Quantum decoherence induced by residual phonons in a ballistic quantum interferometer

Shung-Kang Koh^1*, Ching-Ping Lee², Shi-Xuan Hong², Yung-Fu Chen³, Cen-Shawn Wu⁴, Dah-Chin Ling⁵, Jeng-Chung Chen²

¹Department of Chemistry, National Tsing-Hua University, Hsinchu 30013, Taiwan
²Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan
³Department of Physics, National Central University, Zhongli 32001, Taiwan
⁴Department of Physics, National Chang-Hua University of Education, Changhua 500, Taiwan
⁵Department of Physics, Tamkang University, Tamsui Dist., New Taipei City 25137, Taiwan

* Presenter:Shung-Kang Koh, email:kenkoh190@gmail.com

Understanding the underlying mechanism of quantum decoherence is the central theme in the studies of quantum electronics. It is generally believed that dephasing rate Γ_φ is strongly correlated to the noise spectrum S(f) surrounding the devices. To date, however, there is no consensus regarding the role of S(f) on Γ_φ mainly due to the elusive nature of S(f). In this talk, we will present our recent efforts on exploring the environmental effects– specifically the residual phonons-induced dephasing process in a controlled manner. The device consists of a ballistic Aharonov-Bohm (AB) ring fabricated on GaAs/AlGaAs heterostructure, embedded in a pair of metallic interdigital transducers (IDTs), which is used to launch surface acoustic waves (SAWs).We calibrate the strength of SAWs on Γ_φ via thermal phonons. Our design can be alternatively viewed as placing a quantum interferometer inside a phonon cavity defined by IDTs, whereas the locally trapped phonons is denoted as the residual phonons. Γ_φ extracted from the AB oscillation amplitude (ΔR_AB) measured at 20 mK has been comprehensively is studied as a function of the frequency and intensity of SAWs. We find that Γ_φ (f) is quantitatively scaled with the power spectrum of S_SAW(f). In addition, the relaxation time is saturated at about τ_φ ~ 5ps with phonon power spectrum S_rp(f) ~ 10^-6 aW/Hz. Our work has a strong implication to elaborate the long-standing issue of the phase saturations at low temperatures and to develop an electric contact-free detection technique for semiconductor quantum devices. More results will be presented and discussed.

Keywords: Quantum decoherence, Aharonov-Bohm effect, GaAs/AlGaAs heterostructure