Quantum simulation of an exotic quantum critical point in a two-site charge Kondo circuit

Abstract

The physical properties of a material tuned to the cusp between two distinct ground states can be quite exotic, and unlike those in either of the neighboring phases [1,2]. The prospect of capturing such behavior in a simple model is tantalizing; for example, the interplay between heavy fermion physics and magnetic ordering in certain materials is often rationalized in terms of the quantum phase transition in the two-impurity Kondo model [3,4]. However, this model is oversimplified for the purpose: its quantum critical point does not reflect the distinctive properties of a magnetic lattice surrounded by mobile electrons [5,6]. In this work, we study a tunable nanoelectronic circuit comprising two coupled charge-Kondo quantum islands, realizing a new model which captures the essence of competition between local and collective screening of magnetic moments. This may have relevance for materials in which collective many-body effects drive lattice coherence [7]- [9]. We tune our device to a novel quantum critical point, and show experimentally that deviations as we tune away from this point match non-trivial predictions from the model. This work on the crucial role of inter-island interactions is a necessary first step in scaling up such circuits from individual sites to networks or lattices.

Electronic transport in double-nanowire superconducting islands with multiple terminals

“…Despite the challenges of interwire coupling and low B c , our devices comprise a step towards the realization of exotic proposals in parallel nanowires coupled by superconductors [5,7,[24][25][26] and alternative systems for multichannel Kondo phenomena [63][64][65]. The above limitations can be overcome by employing nanowires well separated from one another integrated by higher B c superconductors such as Pb [53].…”

Two-sites quantum island in the quasi-ballistic regime

“…In Sec. V, we present details on the Bethe ansatz solution for two-sites quantum island and discuss the comparison of our results with the recent experiment [30]. Sec.…”

“…With the analytical description of the quantum critical point, we retrieve many features discussed in Ref. [30] such as: the residual fractional entropy, the scaling exponents close to the triple points and the shape of the conductance as function of the plunger gate voltages. We also predict the emission of fractional charges [44][45][46][47][48] e * = e/3, to be extracted from shot noise measurements [49,50], despite being in the integer quantum Hall regime [51][52][53].…”

“…Recently, a two-site version of the charge Kondo effect has been realized with two coupled metallic islands in a two-dimensional electron gas in a GaAs/AlGaAs heterostructure, and a novel zero-temperature quantum critical point has been identified by comparing experimental data with numerical renormalization group (NRG) calculations [30]. The competition between the screening of each individual island charge and the mediated charge coupling between the two islands may offer an insight on the competition between Kondo screening and collective magnetic ordering in correlated materials.…”

Two-channel charge-Kondo physics in graphene quantum dots

“…More recently, a new nanoelectronics paradigm has emerged, based on charge-Kondo quantum dots [30][31][32][33][34]. In the standard setup, a large QD is coupled at QPCs to source and drain leads.…”