Quantum dot fermi-hubbard emulators
We propose to use semiconductor quantum dot arrays as a well-controlled model system for emulating the Fermi-Hubbard Hamiltonian. In its simplest form, this Hamiltonian contains just two terms, describing hopping of fermions between adjacent sites in a lattice and an interaction energy for two fermions to occupy the same site. Despite its simplicity, this Hamiltonian produces a wealth of many-body physics phenomena, from exotic forms of magnetism to superconductivity. Their intricate quantum correlations make simulation on conventional computers exponentially difficult. This has motivated the use of model systems such as ultra-cold atoms to emulate Fermi-Hubbard physics.  The in-situ parameter control, large energy scales compared to temperature and the flexibility of lithography, make gate-defined quantum dot arrays a highly versatile and powerful model system for emulating Fermi-Hubbard physics. This has long remained a distant prospect due to unavoidable disorder and cross-talk, but recent progress in our lab shows that these obstacles can be overcome in small arrays. This allowed us to observe Nagaoka ferromagnetism, a form of magnetism driven by electron-electron interactions that has not been reported in any system so far.  In a series of breakthrough advances, we will define and operate extended square and triangular quantum dot ladders, targeting a complexity that cannot be matched by classical computers. We will focus on three phenomena at the heart of quantum many-body physics: 1) resonating-valence bond physics at half-filling, 2) doped Mott insulator physics and 3) quantum phase transitions. Besides measuring current through the system, we will perform single-shot measurements of charge and spin, giving access to multi-point correlation functions and time dependent evolution. These studies will increase our understanding of Fermi-Hubbard physics, with long-term application in materials design and discovery.