Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array.

Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi-Hubbard physics on solid-state platforms have been made. Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi-Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

Psychiatric symptoms causing delay in diagnosing childhood cancer: two case reports and literature review.

INTRODUCTION: A somatic disorder may initially be overlooked when a child presents with psychiatric symptoms. We report two children with anorexia nervosa as initial diagnosis and in whom there was a delay in the final diagnosis of the underlying malignancy. A literature survey was performed including patients under 18 years of age with psychiatric symptoms in whom later on an oncological diagnosis became evident as an explanation. RESULTS: We have found 30 additional cases, with a median delay of 12 months until the diagnosis of the tumour. Overall, 16 boys and 16 girls had a solid tumour: 26 central nervous system tumours, 3 tumours of the gastrointestinal tract and 3 others. In 25 out of 32 patients anorexia nervosa was assumed, although it always appeared to be atypical. Patients younger than 7 years had a significantly longer delay until final diagnosis, while no other patient characteristics correlated with such delay. DISCUSSION: In addition to careful physical (including full neurological) examination, we advise additional neuroimaging especially in each case of atypical presentation of anorexia nervosa, in order to avoid a delay in diagnosis of a possible malignancy. Furthermore, it is desirable to perform a re-examination when a psychiatric disorder does not respond to therapy, in order not to overlook an underlying oncological disease.