Aishwarya Lab — Techniques

Our Tools

Instruments

Two complementary setups anchor the lab: an ultra low-temperature scanning tunneling microscope for atomic-resolution spectroscopic imaging, and a nitrogen-vacancy (NV) diamond quantum sensing platform. Every experimental platform offers a different window into quantum materials. Together, they allow us to explore correlated realm of electrons with emergent charge orders, magnetic dynamics across multiple length and time scales.

Illustration of a scanning tunneling microscope and its measurement circuit. A piezoelectric tube scanner holds a metal tip above a sample, with electrons tunneling across the gap; an inset magnifies the tip apex and the tunneling electrons. The circuit shows the tunneling current going through a pre-amplifier to a lock-in amplifier, which returns dI/dV to the computer electronics, and the electronics feeding back to the z-piezo, with AC and DC bias applied to the sample.

Schematic of STM circuit

Setup 01 — Ultra-Low Temperature Scanning Tunneling Microscopy and Spectroscopy (STM/S)

Atomic-resolution mapping of electron wavefunctions

Scanning tunneling microscopy enables direct visualization of the electronic structure of quantum materials with atomic resolution. We are commissioning a Unisoku ULT-STM operating at millikelvin temperatures and in high magnetic fields. Our STM will enable access to the local electronic wavefunctions of quantum materials with exceptional energy and spatial resolution.

Setup 02 — Quantum sensing with NV Centers

Spin-Qubits as nanoscale magnetometers

Nitrogen-vacancy (NV) centers in diamond are atomic-scale spin defects that are robust spin-qubits. We employ them as magnetometers, sensitive enough to image nanoscale magnetic textures, current flow, and spin dynamics without the constraints of tunneling-based probes. This capability is intended to complement our STM system by extending measurements to insulating samples and to a non-contact, non-invasive magnetic-field-sensing modality.

Illustration of nitrogen-vacancy magnetometry. A diamond slab holding NV spins is held above a magnetically ordered sample; a green laser excites the NV centers and red fluorescence is emitted, while field lines run from one NV center down to the alternating red and blue spins of the sample below. An inset shows the NV defect itself — a nitrogen atom beside a vacancy in the carbon lattice.

NV-diamond sensing platform (in development)

Our Tricks

Techniques

Beyond the instruments themselves, the lab develops the probes and measurement methods that make these experiments possible.

False-color scanning electron micrograph of a nanowire tip mounted on an STM probe, annotated to show spin-up electrons travelling down the wire and spin-down electrons travelling up. Scale bar: 10 micrometres.

Topological nanowire tip

Technique 01 — Novel Probes

Customized Scanning Probes

We design and fabricate custom scanning probes for STM using nanofab techniques such as focussed ion beam milling. These tips can be tailored to couple to specific electronic, superconducting or magnetic ground states we are investigating, and can sometimes give rise to unexpected, novel physical phenomena such as axionic tunneling for topological materials.

Technique 02 — Quantum Measurement Control

FPGA-driven control for quantum sensing protocols

Extracting clean, quantitative signal in NV-based magnetometry depends on precise control of measurement conditions. We develop FPGA-based control systems for high-fidelity microwave pulse generation, timing, and synchronization required for advanced quantum sensing protocols. We are working towards arbitrary pulse sequences, real-time experimental control, and rapid implementation of novel sensing techniques for nitrogen-vacancy center magnetometry.

Illustration of an FPGA on a circuit board driving microwave pulse sequences out and receiving readout signals back

FPGA pulse generation and readout