Graphene-based atom chips: a high-performance platform for cold-atom quantum technologies

The project will develop graphene atom chips that reduce (by orders of magnitude) the atom loss rate and spatial scale of the atom trapping potential, as required for portable chip-based quantum sensors. The chips will enable the creation and manipulation of atomic Bose-Einstein condensates with less stringent vacuum pressure requirements than present devices, thus assisting the scalable industry manufacture of chip-based quantum sensors and clocks.
Atom chips use current-carrying microfabricated wires to create a magnetic field and thereby control nearby ultracold atoms. They exhibit robust room-temperature operation and are key components of cold-atom-based quantum sensor/clock technologies1. Existing chips use metallic conductors on bulk substrates. High spatio-temporal noise in the wires, and the large Casimir-Polder attraction of atoms to the substrate, makes the atom clouds fragment and deplete rapidly unless they are held within 5 from the chip. This limits miniaturisation of the chips, the potential landscapes that they produce, and prevents coherent quantum coupling of electrons in the atoms to those in the chips1.
This project aims to transform atom-chip performance by exploiting conductors within two-dimensional electron gases in graphene and other 2D materials. Our recent work indicates that these structures will reduce the atom-surface separation and power consumption of the chip by 2 and 5 orders of magnitude respectively and increase the atom cloud's lifetime by 4 orders of magnitude - to minutes - compared with metallic conductors.
So far, our work has focused on graphene/boron nitride structures, which are promising for transistors and high-frequency electronics2. Using similar structures for atom chips opens the possibility of dual applications in electronic and cold-atom quantum devices. We now need to develop graphene atom-chip demonstrators, based on established materials such as SiC, to demonstrate the power of two-dimensional materials as a platform for quantum sensors and clocks. Existing SiC-based graphene Hall bars3, developed for quantum resistance metrology, look ideal for proof-of-principle studies and subsequent optimisation. The project will develop atom chips based on graphene and other 2D material multilayers by:
1. Calculating atom trap profiles and lifetimes for existing graphene Hall bars, taking into account spatial imperfections and atom loss due to Johnson noise, using Green function models to relate the noise characteristics to the electromagnetic reflection coefficients of the multilayers, tunnelling and 3-body processes.
2. Undertaking detailed analysis of experiments on existing SiC-based Hall bars: both their electrical properties and performance as an atom chip trap.
3. Simulating the dynamics of trapped atom clouds using Stochastic Projected Gross-Pitaevskii models.
4. Designing better samples containing multiple 2D layers to enhance functionality.
5. Undertaking theoretical studies of experiments to be performed on these improved samples by collaborators in Germany.