Krypton tantalum at 200 °C, a superconducting memory light erases and parallel photonic blocks
Three Nature studies advance quantum hardware: qubit-grade tantalum at 200 °C, a gate-written superconducting memory erased by light, and parallel photonic blocks. Each remains a laboratory demonstration.
Science··Morning
Krypton instead of argon grows tantalum to qubit grade at 200 °C
Tantalum thin films have lifted superconducting qubit performance, but depositing the cubic phase directly has generally needed substrate temperatures above 400 °C. A Nature Materials team reports that changing the sputter gas from argon to krypton grows body-centred-cubic tantalum on silicon at temperatures as low as 200 °C. The lower temperature opens a process window compatible with back-end-of-line fabrication standards, which matters because the wiring layers added late in a chip's manufacture cannot survive the hotter recipe. Coplanar-waveguide resonators made from the krypton-sputtered films show a tight performance distribution, while higher-temperature films lose more energy in correlation with how much tantalum and silicon have intermixed. The team also built transmon qubits with a compact 20-micrometre capacitor gap reaching quality factors up to 16.9 million.[1]
Gate cycling writes a superconducting memory that light erases
In aluminium-oxide on potassium-tantalate heterostructures, repeated electrostatic gate cycling promotes the interfacial superconducting state and leaves it in place after the gate is removed, while illumination at cryogenic temperatures erases it, a Nature Communications team reports. The authors attribute both effects to an interplay they say had not been recognised before, between the two-dimensional superconductor at the interface and lattice excitations in the quantum paraelectric substrate: polar nanoregions reorienting, and charge trapped and released by oxygen vacancies. Writing and erasing are both demonstrated at cryogenic temperatures, so the result is a laboratory demonstration of configurable superconductivity rather than a device that could hold a memory at ordinary conditions. It is a rare example of a quantum circuit state that can be written electrically and cleared optically.[2]
One photonic chip splits into blocks running different matrix operations at once
A silicon-on-insulator photonic processor described in Nature Communications can be partitioned into separate functional blocks, each running a different optical matrix operation at the same time, instead of being wired for one fixed task. The demonstration runs three-channel 1×1 and 2×2 real-valued convolution kernels in distinct blocks. The multichannel 1×1 convolution was tested inside a deep residual U-Net segmenting pneumonia lesions in lung computed-tomography images, and the 2×2 convolution inside an optical layer paired with an electrical fully connected layer classifying handwritten digits into ten classes. Both are benchmark tasks run to validate the hardware; neither is a clinical or deployed system. The chip shows that one optical surface can host more than one compute path at the same time.[3]
