arXiv subjects

Harikrishnan Sundaresan

Publications and source records attributed to Harikrishnan Sundaresan.

5 recordsLinked to original sources

arXiv2026

Tunnel-rate controlled local heat distribution in mesoscopic circuits

Solid-state quantum technologies, including qubits and quantum metrology circuits, demand milli-Kelvin operation to preserve fragile quantum states from classical noise. While the negligible electron-phonon coupling is the major impediment, reaching 50 mK electron temperature is further suffered by the high electrical resistance and sub-micron-scale dimensions of typical devices, limiting conventional heat dissipation. Though the phonons are effectively frozen, thermoelectric techniques could offer a viable path for heat management.This work explores thermally driven electrical transport in a gated quantum dot (QD) on a GaAs-AlGaAs two-dimensional electron gas (2DEG), to control heat flow between the source and drain reservoirs.By exploiting the QD's discrete energy spectrum and tuneable tunnel rates, a precise control over the polarity and magnitude of the resulting thermoelectric current is demonstrated. A temperature difference of 650 mK is maintained across the QD, a separation of 400 nm, by tuning the tunnel-rates. An experimental gate pulsing method is also introduced to directly measure the electron temperature differences across the QD, bypassing the need for any theoretical fits. The results presented here show that tuneable tunnel barriers can be used for local heat control, and could lead to advanced quantum refrigerators that work efficiently in mesoscopic circuits.

cond-mat.mes-hall↗

arXiv2026

Cascaded Four-Wave Mixing on Quantum Paraelectrics for On-chip Cryogenic Microcombs

Here, we demonstrate an on-chip cryogenic microwave frequency-comb on a planar superconducting resonator fabricated on Strontium titanate(STO), a quantum paraelectric material. The material's Kerr-type nonlinearity arising from the quantum paraelectric phase, an underexplored state, enables pronounced resonance shifts, Duffing-like bifurcations and comb generation via cascaded foure-wave mixing. Our results establish STO resonators as a low power, cryogenically compatible platforms for nonlinear microwave photonics, with applications in scalable quantum control and on-chip frequency synthesis.

cond-mat.mes-hall↗

arXiv2026

Cryogenic microwave frequency combs based on quantum paraelectric superconducting resonators

A frequency comb, known for its precision as an "optical ruler", features an evenly spaced spectral pattern. While these combs are vital in photonic quantum technologies, their microwave counterparts are now highly sought after for cryogenic quantum technologies, including semiconducting and superconducting qubits and quantum electrical metrology, which mainly operate in the microwave regime. However, microwave combs are still largely underexplored, and typically rely on complex, high-power optical systems incompatible with the low-power, cryogenic on-chip quantum technologies. In this manuscript, we present an all-electrical, on-chip, cryogenic microwave frequency comb on Strontium Titanate (SrTiO$_3$), exploiting its Pockels-like effect in its quantum paraelectric phase. Our device, utilizing a superconducting microwave cavity, generating the frequency comb via cavity phase modulation enabled by the field-induced effective $χ(2)$ of SrTiO$_3$. The ability to continuously vary the dielectric constant of SrTiO$_3$ by the application of electric field, in its quantum paraelectric phase, makes it possible to control the comb's operating frequency range. The exceptionally high dielectric constant of SrTiO$_3$, > 20,000 in its quantum paraelectric state, enables an ultra-miniature design and on-chip integration with cryogenic quantum technologies.

cond-mat.mes-hall↗

arXiv2025

Active Noise Reduction in Si/SiGe Gated Quantum Dots

Solid-state quantum technologies such as quantum dot qubits and quantum electrical metrology circuits rely on quantum phenomena at ultra-low energies, making them highly sensitive to various forms of environmental noise. Conventional passive filtering schemes can reduce high-frequency noise but are often ineffective against low-frequency interference, like powerline or instrument-induced. Extending such filters to lower frequencies causes practical issues such as longer stabilization times, slower system response, and increased Johnson noise, which impede low-frequency transport measurements. To address these limitations, we propose and experimentally demonstrate a generalized active noise cancellation scheme for quantum devices operating at sub-Kelvin temperatures. Our approach compensates periodic environmental interference by dynamically injecting a phase-coherent anti-noise signal directly into the device. We employ an automated feedback protocol featuring beat-frequency reduction and adaptive phase-amplitude tuning, enabling real-time compensation without any manual intervention. Unlike post-processing or passive filtering, this method suppresses noise at the device level without introducing additional time constants. We implement the scheme on a gate-defined Si/SiGe quantum dot subject to strong 50 Hz powerline interference and validate its effectiveness through acquiring Coulomb Blockade Oscillations and Coulomb diamond plots. The technique achieves substantial suppression of both the targeted interference and the overall noise floor, thereby stabilizing transport characteristics and enhancing device fidelity. While demonstrated on a quantum dot, the proposed framework is broadly applicable to a wide class of solid-state quantum devices where deterministic noise presents a critical bottleneck.

cond-mat.mes-hall↗

arXiv2023

GHz operation of a quantum point contact using stub impedance matching circuit

Quantum point contacts (QPC) are the building blocks of quantum dot qubits and semiconducting quantum electrical metrology circuits. QPCs also make highly sensitive electrical amplifiers with the potential to operate in the quantum-limited regime. Though the inherent operational bandwidth of QPCs can eclipse the THz regime, the impedance mismatch with the external circuitry limits the operation to a few kHz regimes. Lumped-element impedance-matching circuits are successful only up to a few hundreds of MHz. QPCs are characterised by a complex impedance consisting of quantized resistance, capacitance, and inductance elements. Characterising the complex admittance at higher frequencies and understanding the coupling of QPC to other circuit elements and electromagnetic environments will provide valuable insight into its sensing and backaction properties. In this work, we couple a QPC galvanically to a superconducting stub tuner impedance matching circuit realised in a coplanar waveguide architecture to enhance the operation frequency into the GHz regime and investigate the electrical amplification and complex admittance characteristics. The device, operating at 1.96 GHz exhibits a conductance sensitivity of 29.2 micro-e/SQRT(Hz) and a bandwidth of 13MHz. Besides, the RF reflected power unambiguously reveals the complex admittance characteristics of the QPC, shining more light on the behaviour of quantum tunnel junctions at higher operational frequencies.

cond-mat.mes-hall↗