Quantum decoherence induced by residual phonons in a ballistic quantum interferometer
Shung-Kang Koh1*, 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 Γφ 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 Γφ 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 Γφ 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. Γφ extracted from the AB oscillation amplitude (ΔRAB) measured at 20 mK has been comprehensively is studied as a function of the frequency and intensity of SAWs. We find that Γφ (f) is quantitatively scaled with the power spectrum of SSAW(f). In addition, the relaxation time is saturated at about τφ ~ 5ps with phonon power spectrum Srp(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