Low-frequency noise in transport through quantum point contacts

We report the noise characteristics of quantum point contacts between 100 Hz and 100 kHz at 4.2 K. The noise consists of a 1/f component on top of a white background. The 1/f noise increases as the contact width decreases and shows peaks between the quantized resistance plateaus. The white noise background increases with current but is much lower than the full shot noise level, suggesting that shot noise is not generated in an ideal quantum point contact, where the electrons do not suffer backscattering as they enter and traverse the contact.