Praveen Sriram

Controlled experimental realizations of simplified effective Hamiltonians are key to understanding the behavior of quantum many-body systems. Cold atoms in optical lattices,  trapped ions, superconducting circuits, and semiconductor quantum dots are popular platforms deployed in this context, and each have distinctive advantages. Using any of these systems to model electrons in a bulk crystal has been challenging, typically limited by inability to cool to a many-body ground state (AMO systems) or inhomogeneity among sites as one tries to scale to a sizable array (semiconductor dots). Hybrid metal/semiconductor structures have recently enabled unprecedented control of exotic quantum critical points[1], and our group has shown that this can be extended beyond a single site coupled to a reservoir [2]. Incorporating metal islands in place of semiconductor quantum dots can allow each site to behave basically identically. Work to date has been based on GaAs heterostructures, where the metal islands must be annealed to contact the semiconductor. Consequently, the islands cannot be made smaller than a few microns, limiting charging energies and thus restricting scaling studies to below 50 mK, less than 10x above the coldest electron temperatures. The surface Fermi-level pinning in InAs affords direct ohmic contact to non-annealed sub-micron islands with large charging energies, offering the possibility of measurement over a 10x broader temperature range.  We have demonstrated highly transparent interfaces (>99%) between quantum Hall edge states and sub-micron metal islands, and clean quantum point contacts (QPCs)[3] in a high-mobility (10$^6$ cm$^2$/Vs) InAs quantum well grown on InP. Despite the lattice-mismatch with the substrate, our QPCs are the cleanest amongst the handful of reported works in InAs and InGaAs, with up to eight quantized conductance plateaus. These building blocks enable the design of hybrid InAs/metal islands -- and arrays of effectively identical islands with tunable interactions -- for simulating quantum criticality and gaining insight into Kondo lattice coherence.

*This work is supported by the U.S. Department of Energy,  Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract DE-AC02-76SF00515.

[1] Iftikhar, Z. et al. Tunable quantum criticality and super-ballistic transport in a “charge” Kondo circuit. Science 360, 1315–1320 (2018).
[2] Pouse, W. et al. Exotic quantum critical point in a two-site charge Kondo circuit. arXiv:2108.12691 (2021).
[3] Hsueh, C.L., Sriram, P. et al. Phys. Rev. B 105, 195303 (2022).