Quantum computing is often hailed as the future of complex problem-solving, particularly for its potential to disrupt current encryption systems. However, a significant challenge in advancing the field is scaling quantum computers to millions of qubits, which is crucial for fully error-corrected algorithms and noisy intermediate-scale quantum applications.
Existing methods for manipulating and reading qubits are costly and complex, primarily because they rely on routing microwave signals through coaxial cables from room-temperature electronics to quantum chips in cryogenic dilution fridges. This setup becomes impractical and expensive when scaling beyond about 1,000 qubits due to increased costs and heat dissipation issues.
One proposed solution to this problem is monolithic integration. This approach involves tightly integrating qubits with control and microwave electronics, thereby replacing traditional wiring with chip stackings and circuit blocks.
Monolithic integration can reduce both passive heat load and the system’s footprint while improving signal fan-out and fan-in capabilities and minimizing communication latency. However, this method requires a compatible cryogenic microwave pulse generator.
Recent research offers a promising development in this area: an on-chip coherent cryogenic microwave pulse generator. This new device generates pulsed microwave emissions with controlled phase, intensity, and frequency directly at millikelvin temperatures.
It operates using superconducting circuits within a vacuum process, allowing precise control of these parameters through digital manipulation of magnetic flux across a superconducting quantum interference device (SQUID) embedded in a superconducting resonator.
The device features a ?/2 coplanar waveguide resonator with a SQUID in its center conductor. The SQUID, equipped with two parallel Josephson junctions, functions as a tunable inductor, adjusting the resonator’s properties by varying the magnetic flux.
This setup, combined with a three-dimensional circuit quantum electrodynamics architecture, optimizes the readout process. Experiments with room temperature junction resistances, ranging from 50 ? to 270 ?, showed inductance values that contributed to the total inductance of the SQUID-embedded resonators.
The pulse generator was driven by an arbitrary waveform generator with a 1 GHz sampling rate, providing the necessary flux steps to the signal source in the cryogenic environment. The output was amplified through multiple temperature stages.
The innovation of the on-chip coherent cryogenic microwave pulse generator represents a significant advance in generating microwave photon pulses with high coherence. This breakthrough not only improves the performance of microwave photon sources in cryogenic environments but also holds the potential to facilitate the large-scale implementation of superconducting quantum computers.