Qtran Lab
at IISER Thiruvananthapuram
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Welcome to QTran Lab
Cryogenic microwave frequency combs basedon quantum paraelectric superconductingresonators (Editorial pick)
A frequency comb, known for its precision as an “optical ruler,” features an evenly spaced spectral pattern. While these combs are vital in integrated photonics, their microwave counterparts are now highly sought in cryogenic quantum technologies, including semiconducting and superconducting qubits as well as quantum electrical metrology. However, microwave combs are still largely underexplored. In this work, we present an all-electrical, on-chip, cryogenic microwave frequency comb on strontium titanate (STO), exploiting its Pockels-like effect in its quantum paraelectric phase. The device utilizes a superconducting microwave cavity to generate the frequency comb via cavity phase modulation enabled by the field-induced effective χ(2) of STO. The ability to continuously vary the dielectric constant of STO by the application of an electric field, in its quantum paraelectric phase, makes it possible to control the comb’s operating frequency span. The exceptionally high dielectric constant of STO > 20 000 at low temperatures, enables an ultra-miniature design and on-chip integration with cryogenic quantum technologies.
Read More: https:/doi.org/10.1063/5.0349286
Valley splitting and density-driven scattering in undoped Si/SiGe two-dimensional electron system
Using low-temperature magnetotransport measurements, we investigate impurity scattering and valley splitting in a high-mobility, undoped Si/SiGe two-dimensional electron gas. Carrier lifetimes are governed by both remote charged impurities and background impurities, but increase with carrier density due to enhanced screening by the electron gas. Magnetic-field-induced orbital confinement further enhances the valley splitting. These findings provide important insights into transport and valley physics in undoped Si/SiGe, supporting its potential for silicon-based quantum devices.
Read More: https:/doi.org/10.1088/1361-648X/ae8fae
Tunnel-rate controlled local heat distribution in mesoscopic circuits
While solid-state quantum technologies demand milli-Kelvin operation, the thermalization and cooling of a two-dimensional electron gas remain challenging due to the weak electron-phonon scattering in these systems at low temperatures. This work demonstrates gate-tunable control over heat flow between two points in a GaAs/AlGaAs two-dimensional electron gas, using the discrete energy spectrum and tunable tunnel rate of a quantum dot in between. Temperature differences of up to ~650 mK are demonstrated to be maintained across a separation of ~400 nm, suggesting prospects for tunable, on-chip methods for local heat distribution. We also demonstrate a gate-pulsing method that enables an experimental estimate of the electron temperature difference across the quantum dot.
Read More: https:/doi.org/10.1088/2058-9565/ae8a79
Cryogenic microwave mixing and phase control in superconducting quantum paraelectric resonator
Our latest publication demonstrates cryogenic microwave frequency mixing and phase control using a superconducting resonator on strontium titanate (STO). By harnessing the strong dielectric tunability and nonlinear properties of STO in its quantum paraelectric state, we realize a sub-Kelvin microwave mixer and voltage-controlled phase shifter capable of efficient frequency conversion, spectral shaping, and microwave signal processing at millikelvin temperatures.
Read More: https:/doi.org/10.116/j.xcrp.2026.103387
Engineering robust Supercurrent rectification and damping charecteristics in NbSe2-NbSe2 van der Waals Josephson junction
Field-resilient supercurrent rectification in NbSe2 van der Waals Josephson junction
Superconducting systems, such as thin films and Josephson junctions, void of both inversion and time-reversal symmetries, are explored in this regard. While the Pauli paramagnetic field limit puts an upper bound on observing supercurrent rectification, the demonstrated functionalities are limited to only low magnetic fields. In contrast, many quantum and classical technologies require operation at higher magnetic fields. In this work, we present an NbSe2–NbSe2 van der Waals Josephson junction diode, exhibiting supercurrent rectification in a wide range of magnetic fields. For lower magnetic fields, the supercurrent rectification efficiency increases with the magnetic field and saturates to ∼40% for fields ∼1 T and beyond.
For more details: DOI 10.1088/2053-1583/ae403f
Active noise reduction in gated quantum devices
Solid-state quantum devices are highly sensitive to low-frequency noise that passive filters cannot remove without degrading signals. We suppress 50 Hz interference in a sub-Kelvin Si/SiGe quantum dot by injecting phase-coherent anti-noise. Automated feedback adaptively tunes phase and amplitude, lowering the noise floor and stabilizing transport measurements. This method can be generalized to noise-sensitive solid-state quantum platforms.
For more details: doi.org/10.1063/5.0303853
A strategy for realizing van der Waals Josephson junction arrays
Noise, beyond a few kHz, can be effectively filtered by an array of low-pass filters operated at various temperature stages. Minimizing noise in the lower frequency bands presents a significant challenge, particularly in experiment-specific voltage sweeps, where the sweep duration is susceptible to low-frequency periodic noise or 1/f noise having long-term correlations. This paper addresses this gap by introducing a predictive noise cancellation strategy for improved noise mitigation in short-term voltage sweeps. Our system consists of a home-built microvolt precision, dual digital-to-analog converter (DAC). The dual-DAC strategy allows control and compensation in the milli- and microvolt range with better noise isolation independently.
For more details: DOI: 10.1039/d5nr03782d
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Reach out to us
Feel free to get in touch with us!
Lab
Room No. 1203,
Physical Sciences Block,
IISER Thiruvananthapuram
Phone: 0471 2778085
Email: qtran@iisertvm.ac.in
Office
Room No. 2202,
Physical Sciences Block,
IISER Thiruvananthapuram
Phone: 0471 2778084
Email: madhu@iisertvm.ac.in
Funding and Support
We gratefully acknowledge the financial backing and collaboration from our sponsors. Their contributions play a pivotal role in advancing our research, enabling us to investigate the intricate world of quantum transport and its potential applications.
Team
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Principal Investigator
Dr. Madhu Thalakulam
https://scholar.google.com/citations?user=3--YLbIAAAAJ&hl=en&oi=aoResearch Interests:
- Quantum transport: Transport in nanoscale devices such as QPCs, quantum dots, superconducting tunnel junction systems.
- High-frequency measurements: Radio-frequency reflectometry of nanoscale devices such as QPCs, Quantum dots etc.
- Solid state qubits: Single spin manipulation and detection in quantum dot qubits. Quantum measurement and back action in nanoscale devices.
- Devices on van der Waals materials and heterostructures
- Topological Insulators (TI) and TI based devices for spintronics
Contact:
+91 (0)471 - 2778084
Email:
madhu@iisertvm.ac.in
Education:
Ph.D. Applied Physics (Rice Quantum Institute, Rice University, Houston TX, May 2007. )
Education:
PhD from Central University of Kerala, Kasaragod
Integrated PhD Student
Hari Krishnan S
Research Interests:
- Working towards the realisation of semiconducting spin qubits for quantum computing, which involves hybrid circuit QED where quantum dots are coupled to microwave resonators for qubit control, readout and long range spin-spin coupling.
Contact:
Email:
sharik18@iisertvm.ac.in
Education:
B.Sc (Physics), Loyola College (Affiliated to University of Madras)
Doctoral Student
Parvathy Gireesan
Research Interests:
Gated quantum dot systems on GaAs/AlGaAs heterostructures: thermally driven and noise-driven ratchet currents at zero-bias
Developing gated quantum dot systems on MoS2
Integrating vdW layered systems like MoS2 with quantum dot structures on GaAs/AlGaAs
Contact:
Email:
parvathygireesan21@iisertvm.ac.in
Education:
Integrated BS-MS dual degree, with major in Physics and minor in Mathematics, from IISER-THIRIVANANTHAPURAM
