Reducing decoherence in quantum computers rapidly decreases the overhead needed to construct a logical qubit from physical qubits. In solid-state systems, a class of defects known as two-level systems is a major source of decoherence. Currently, superconducting qubit experiments reduce dissipation due to the two-level systems by using large device dimensions. However, this approach only provides partial protection and results in a trade-off between qubit size and dissipation. In this work, we instead engineer the interactions between a qubit and the surrounding two-level systems using phononics. We fabricate a superconducting qubit on a phononic-bandgap metamaterial that suppresses phonon emission mediated by the two-level systems. The phonon-engineered bath of two-level systems shows increased lifetime and affects the thermalization dynamics of the qubit. Within the phononic bandgap, we observe the emergence of a non-Markovian qubit behaviour. Combined with qubit miniaturization, our approach could substantially extend the qubit relaxation times. Defects known as two-level systems are a major source of noise for superconducting qubits. Adding a phononic crystal is now shown to extend the lifetime of these two-level systems, which could lead to improved qubit coherence.

The development of superconducting quantum processors relies on understanding and mitigating decoherence in superconducting qubits. Piezoelectric coupling contributes to decoherence by mediating energy exchange between microwave photons and acoustic phonons. Although bulk centrosymmetric materials like silicon and sapphire are non-piezoelectric and commonly used as qubit substrates, the lack of centrosymmetry at interfaces may induce piezoelectric losses. This effect was predicted decades ago but never experimentally observed in superconducting devices. Here, we report interface piezoelectricity at aluminum-silicon junctions and demonstrate it as a significant loss channel in superconducting devices. Using aluminum interdigital transducers on silicon, we observe piezoelectric transduction from room to millikelvin temperatures, with an effective electromechanical coupling factor K2 ≈ (3 ± 0.4) × 10-5%, comparable to weakly piezoelectric substrates. Modeling shows this mechanism limits qubit quality factors to Q ~ 104 - 108, depending on surface participation and mode matching. These findings reveal interface piezoelectricity as a major dissipation channel and highlight the need for heterostructure and phononic engineering in next-generation superconducting qubits.

The performance of superconducting quantum circuits is primarily limited by dielectric loss due to interactions with two-level systems (TLS). State-of-the-art circuits with engineered material interfaces are approaching a limit where dielectric loss from bulk substrates plays an important role. However, a microscopic understanding of dielectric loss in crystalline substrates is still lacking. In this work, we show that boron acceptors in silicon constitute a strongly coupled TLS bath for superconducting circuits. We discuss how the electronic structure of boron acceptors leads to an effective TLS response in silicon. We sweep the boron concentration in silicon and demonstrate the bulk dielectric loss limit from boron acceptors. We show that boron-induced dielectric loss can be reduced in a magnetic field due to the spin-orbit structure of boron. This work provides the first detailed microscopic description of a TLS bath for superconducting circuits, and demonstrates the need for ultrahigh purity substrates for next-generation superconducting quantum processors.

We characterize coherence of single photons emitted from a G center in a silicon waveguide. We present progress towards lifetime-limited and frequency-tunable single photon emission via electrical tuning.

In this work, we investigate the scattering behavior of nanorods that are randomly packed at various densities and aspect ratios. We show that the maximum packing density, maximum scattering density, and the percolation threshold are all tightly related to Onsager excluded-area principle.

We present our latest work and investigation of exceptional point in plasmonic nanostructures. We show that the non-Hermitian singularity can be effectively deployed in small scale sensors and pave the path for engineering metamaterials with novel properties.

Resonant scattering, guided mode propagation phase, and/or orientation-dependent phase retardations are the three main mechanisms used to date to conceive optical metasurfaces. Here, we introduce an additional degree of freedom to address optical phase engineering by exploiting the topological features of non-Hermitian matrices operating near their singular points. Choosing metasurface building blocks to encircle a singularity following an arbitrarily closed trajectory in parameter space, we engineered a topologically protected full 2π-phase on a specific reflected polarization channel. The ease of implementation together with its compatibility with other phase-addressing mechanisms bring topological properties into the realm of industrial applications at optical frequencies and prove that metasurface technology represents a convenient test bench to study and validate topological photonic concepts.

A compact and high performance integrated silicon TM-pass polarizer is proposed and experimentally demonstrated. The device is formed by periodically structuring a waveguide with a slot section within each period, and is implemented on a siliconon-insulator platform. The fabricated device has low insertion loss for the TM mode (average 0.7dB) and high extinction for the TE mode (average 41.25dB), over a 1.5 μm to 1.6 μm wavelength range. Numerical simulations indicate that a large fraction of the blocked TE mode radiates out of the periodic structure, resulting in weak back reflections. The compact footprint of the device (21 μm × 0.5 μm) makes it suitable for dense integration in photonic integrated circuits.

Random jammed dipole scatterers are natural composite and common byproducts of various chemical synthesis techniques. They often form complex aggregates with nontrivial correlations that influence the effective dielectric description of the medium. In this work, we investigate the packing dynamic of rectangular nanostructure under a close packing protocol and study its influence on the optical response of the medium. We show that the maximum packing densities, maximum scattering densities, and percolation threshold densities are all interconnected concepts that can be understood through the lens of Onsager’s exclusion area principle. The emerging positional and orientational correlations between the rectangular dipoles are studied, and various geometrical connections are drawn. The effective dielectric constants of the generated ensembles are then computed through the strong contrast expansion method, leading to several unintuitive results such as scattering suppression at maximum packing densities, as well as densities below the percolation threshold, and maximum scattering in between.

In this paper, we investigate the mode sensitivity (S-mode) of subwavelength grating slot (SWGS) waveguides. S-mode is an important parameter in various waveguide-based photonic circuits such as sensors, modulators, and thermally-controlled devices. It is a measure of the sensitivity of the waveguide effective index towards the refractive index perturbations in the cladding medium. The SWGS waveguide exhibits high mode sensitivity, as it combines sensitivity enhancement features of both slot and subwavelength grating waveguides. Finite-difference time-domain simulations are performed for the analysis, design, and optimization of the hybrid structure. The SWGS waveguide is incorporated into a Mach-Zehnder interferometer and fabricated on a silicon-on-insulator platform for the experimental estimation of S-mode. The measured S-mode value of 79% is consistent with the theoretical prediction of 83%.

We demonstrate a compact (21 μm × 0.5 μm) silicon TM-pass polarizer based on a slot-assisted periodic waveguide. Measured results show low insertion loss for the TM mode (average 0.7 dB) and high TE loss (average 41.3 dB) over a 100 nm wavelength range, centered at 1.55 μm.

This work demonstrates an approach for simplifying fiber-to-chip (edge coupling) packaging by virtually eliminating the longitudinal alignment procedure (also increasing compactness and efficiency) through a fiber lens embedded into the structure of the fiber itself. A parabolic lens, fabricated using focused ion beam milling, with a diameter of 15 mu m and height of 5 mu m, was embedded 6.5 mu m (the working distance of the parabolic lens) below the endfacet of the fiber. The lens focuses a 10.4 mu m fiber mode into a spot size of 2.6 mu m on the surface of an SMF-28e single-mode optical fiber. The properties of the fabricated lens were studied using the three-dimensional finite-difference time-domain numerical method, and the optimal parameters for maximizing the coupling conditions were extracted. The conversion loss of the lens is estimated to be around 0.5dB. The insertion loss and lateral alignment of the proposed parabolic lens is comparable to a commercial lensed fiber, while directly ensuring the longitudinal alignment, easing the angular alignment, and providing additional mechanical and environmental robustness.

We experimentally demonstrate a slotted subwavelength grating (SSWG) waveguide on a silicon-on-insulator platform. The waveguide was included in an asymmetric Mach-Zehnder interferometer, and a fluid sensing experiment was performed. The estimated mode sensitivity (79 %) is consistent with the simulation results (83 %). The high mode sensitivity of the SSWG waveguide makes it suitable for compact integrated optofluidic sensors.

We propose a microfluidic channel with a rectangular cross-section, built on a polydimethylsiloxane substrate that also acts as a waveguide through a controlled gradient refractive index profile, fabricated by a modified soft-lithography technique.

We propose an alignment-free fabrication process to realize two-level photonic structures using a bilayer resist. The high contrast of the resist is preserved, and the technique can therefore be used in integrated nanophotonics.

We demonstrate a gradient-index (GRIN) optofluidic waveguide using polydimethylsiloxane cured with a radial variation of temperature. The waveguide wraps the microfluidic channel and the GRIN profile localizes the light around it, making the device suitable for evanescent sensing applications. The fabricated waveguide shows good light confinement, with a propagation loss of 1.47 dB/cm at a wavelength of 632.8 nm.

We demonstrate a novel monolithic graded index (GRIN) waveguide with a concentric microfluidic channel using polydimethylsiloxane (PDMS) cured with a radial variation of temperature. The measured propagation loss is 1.47dB/cm at 632.8 nm.

This paper presents a low power, high data rate transceiver for passive RFID tags. Asymmetric communication link between the reader and the tag was employed to overcome the passive systems׳ power constraints while providing higher data rates. For the uplink, a low power, digital Impulse Radio Ultra-wideband (IR-UWB) transmitter was employed to send large amounts of data from the several tags to the reader while maintaining the low power requirements. The uplink can achieve data rates as high as 100 Mbps using BPSK modulation. On the other hand, the ISM band was used for the downlink. The downlink features slower data rate of 100 Kbps and utilizes a new modulation scheme that is more suitable for passive systems. The proposed transceiver was designed and simulated in 28-nm CMOS technology.

This paper presents the design and simulation of the front-end low power transmitter for wireless sensor network application. The transmitter features simple circuitry with circuit techniques that reduce the power consumption and gives higher efficiency. The used modulation scheme is a modified version of ASK with better continuity to make it eligible for Wireless Passive Sensor Networks applications. The proposed transmitter features simple circuitry (smaller size), It operates in the ISM band (902-928 MHz) at 50 Kbps data rate. It achieves -6 dBm output power consuming 1.13 mW from a 1.8 V power supply. It was implemented and simulated using 0.18 um CMOS technology.