TOPSQUAD aims at demonstrating that strongly interacting holes in Ge wires with a Si shell are a compelling platform for scalable and topologically protected quantum bits. The objectives of TOPSQUAD are:

1. To grow a topological material – Ge wires – purposely engineered with the properties crucial to realize topologically protected quantum states.


(a) Ge/Si core/shell wires.                           (b) Ge hut wires.  

2. To demonstrate those properties in low-temperature transport measurements and to induce superconductivity in the wires while retaining those important properties.

(a) Josephson field effect transistor. (b) Ge/Si core/shell nanowire

3: To establish the emergence of Majorana zero modes in single-wire and double-wire devices.

(a) Ge hut wires on Si wafers with patterned trenches. b) The principle of Selective Area Growth (SAG) of Ge channels in a SiNx mask on a Si(100)  substrate. c) an envisioned structure to be grown by SAG with indicated crystal growth directions.


(a) Double-wire layout with 4 terminals. Inset: Two Ge wires grown on side of an etched trench; (b) Schematic of a three terminal site-controlled hut wire device.