Controlling charge quantization with quantum fluctuations

• Published in: Nature (London) 2016-08, Vol.536 (7614), p.58-62
• Main Authors: Jezouin, S., Iftikhar, Z., Anthore, A., Parmentier, F. D., Gennser, U., Cavanna, A., Ouerghi, A., Levkivskyi, I. P., Idrisov, E., Sukhorukov, E. V., Glazman, L. I., Pierre, F.
• Format: Article
• Language: English
• Subjects: 639/766/1130/2798; 639/766/119/1000/1018; 639/766/119/995; 639/766/483/1139; 639/925/927/1007; Analysis; Electrons; Fluctuations; Humanities and Social Sciences; Hybrids; letter; multidisciplinary; Physics; Quantum computing; Quantum physics; Quantum theory; Science
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature19072

A device consisting of a metallic island connected to electrodes via tunable semiconductor-based conduction channels is used to explore the evolution of charge quantization in the presence of quantum fluctuations; the measurements reveal a robust scaling of charge quantization as the square root of the residual electron reflection probability across a quantum channel, consistent with theoretical predictions. A model of charge quantization evolution The charge of a single electron or proton defines the fundamental unit of electric charge. But in nanoelectronic devices, where quantum fluctuations are in play, the discreteness of this elementary charge is eroded with increasing connection strengths between conducting elements. Fundamental predictions have been difficult to verify, but now Frédéric Pierre and colleagues have constructed a device, consisting of a micrometre-scale metallic island connected to electrodes via fully controllable semiconducting channels, where the complete evolution of charge quantization can be measured. The work confirms long-standing theory and opens up a platform for testing charge quantization in challenging scenarios involving correlated electrons and topological quasiparticles. In 1909, Millikan showed that the charge of electrically isolated systems is quantized in units of the elementary electron charge e . Today, the persistence of charge quantization in small, weakly connected conductors allows for circuits in which single electrons are manipulated, with applications in, for example, metrology, detectors and thermometry 1 , 2 , 3 , 4 , 5 . However, as the connection strength is increased, the discreteness of charge is progressively reduced by quantum fluctuations. Here we report the full quantum control and characterization of charge quantization. By using semiconductor-based tunable elemental conduction channels to connect a micrometre-scale metallic island to a circuit, we explore the complete evolution of charge quantization while scanning the entire range of connection strengths, from a very weak (tunnel) to a perfect (ballistic) contact. We observe, when approaching the ballistic limit, that charge quantization is destroyed by quantum fluctuations, and scales as the square root of the residual probability for an electron to be reflected across the quantum channel; this scaling also applies beyond the different regimes of connection strength currently accessible to theory 6 , 7 , 8 . At increased temperatures, the the