Research

Quantum Nanomechanics

Our core research is focussed on building and exploring quantum states of nanomechanical resonators. To do this, we used a tool called “optomechanics”. Optomechanics is a technique in which one can use light trapped in a cavity to probe and control the motion of a mechanical resonator at the quantum level.

In the SteeleLab, the main focus of our research is implementing optomechanical systems using mechanical resonators and microwave photons. To do this, we use low-loss superconducting devices operating at millikelvin temperatures that resonate at microwave frequencies and can trap microwave photons for long periods of time. In these superconducting devices, we engineer a coupling of the trapped microwave fields to the motion of a high quality-factor mechanical resonator that oscillates at frequencies in the range of kHz to MHz. Using the coupling of these microwave photons to phonons in the mechanical object, we aim to cool the mechanical resonator to it’s quantum ground state and detect it’s motion with quantum sensitivity by looking at the microwave “light” that comes back out.

To trap the microwave light, we use a wide range of superconducting cavities, ranging from coplanar waveguides and 3D microwave cavities to superconducting resonant devices based on the Josephson effect, such as transmon qubits and SQUID LC resonators. As mechanical resonators, we explore things like ultra-thin drums made from graphene and 2D crystals, millimeter sized membranes and high-tensile strings made from silicon nitride, and more exotic materials such as carbon nanotubes.

The following references give a feel for the type of optomechanics work we do (see our publications page for a complete list):

Large cooperativity and microkelvin cooling with a 3D optomechanical cavity
Mingyun Yuan, Vibhor Singh, Yaroslav M. Blanter, Gary A. Steele
arxiv

Optomechanical coupling between a graphene mechanical resonator and a superconducting microwave cavity
V. Singh, S. J. Bosman, B. H. Schneider, Y. M. Blanter, A. Castellanos-Gomez, G. A. Steele
Nature Nanotechnology 9, 820 (2014) arxiv

Quantum Transport in Carbon Nanotubes

Few electron quantum dots and nanotube Josephson Junctions

In the SteeleLab, we have developed technology for making extremely high quality suspended nanotube devices in which the ultra-clean nanotubes can be connected to metal contacts to make micron-sized few-electron and few-hole quantum dots, and to superconductors to make long ballistic Josephson junctions. Using these devices, we explore the physics of the clean, low density limit of one-dimensional conductors.

For a recent overview, see:

Quantum transport in carbon nanotubes
E.A. Laird, F. Kuemmeth, G. Steele, K. Grove-Rasmussen, J. Nygård, K. Flensberg, L.P. Kouwenhoven
Rev. Mod. Phys. 87, 703 (2015) arxiv

Collaborations

2D semiconductors (Andres Castellanos, Herre van der Zant)

Pioneered by former SteeleLab member Andres Castellanos, we use a deterministic stamping technique to build stacks and heterostructures out of a wide range of 2D crystalline materials, including 2D metals like graphene, 2D superconductors such as TaS2, 2D insulators such as Boron Nitride, and 2D semiconductors such as MoS2 and WSe2. We study the optoelectronic response of these materials to a wide range of illumination wavelengths, observing effects such a strain tuning of the bandgap and large photothermoelectric voltages. In future work, we plan to expand this to explore the response of things like PN junctions to circularly polarized light, probing effects such as the ambipolar Valley Hall effect in crystals with broken symmetry.

2D material highlights:

Photovoltaic effect in few-layer black ​phosphorus PN junctions defined by local electrostatic gating
Michele Buscema, Dirk J. Groenendijk, Gary A. Steele, Herre S.J. van der Zant, Andres Castellanos-Gomez
Nature Communications 5, 4651 doi: 10.1038/ncomms5651 (2014) arxiv

Local Strain Engineering in Atomically Thin MoS2
Andres Castellanos-Gomez, Rafael Roldán, Emmanuele Cappelluti, Michele Buscema, Francisco Guinea, Herre S. J. van der Zant, and Gary A. Steele
Nano Letters 13, 5361 (2013) arxiv

Large and Tunable Photothermoelectric Effect in Single-Layer MoS2
Michele Buscema, Maria Barkelid , Val Zwiller , Herre S. J. van der Zant , Gary A. Steele, and Andres Castellanos-Gomez
Nanoletters 13, 358 (2013) arxiv

Probing materials with microwave cavities

A new direction we are exploring is using the superconducting cavity technology we have developed for optomechanics to couple to electrons and spins in materials, such as single-molecule magnet crystals (collaboration with Herre van der Zant), LAO/STO superconducting interfaces (collaboration Andrea Caviglia), and high quality encapsulated graphene (collaboration Lieven Vandersypen).

Room temperature nanomechanics (Peter Steeneken, Herre van der Zant)

We maintain a strong collaboration with Peter Steeneken and Herre van der Zant to study the mechanics of 2D membranes at room temperature with the goal of exploring applications and understanding the nanomechanical response of these devices.