Inside a room at Lawrence Berkeley National Laboratory, a golden chandelier-shaped apparatus keeps quantum processors cooler than the vacuum of outer space—below 20 millikelvin, hovering just 0.02 degrees above absolute zero. This extreme cryogenic dilution refrigerator is just one piece of a larger puzzle that researchers are solving to build the next generation of quantum computers.
Quantum computing promises to revolutionize science, accelerating breakthroughs in drug development, cosmology, materials science, and nuclear physics. But getting from promise to reality requires more than cutting-edge qubits alone. It demands what researchers call a complete quantum computing "stack"—an integrated technology ecosystem of hardware, software, and control systems designed to work in perfect harmony.
Chris Spitzer, operations lead at Berkeley Lab's Advanced Quantum Testbed (AQT), explains the architecture. At the foundation sits a superconducting quantum processing unit containing the qubits that store and manipulate quantum information. Above it rests the dilution refrigerator's cold stage, an engineering marvel that resembles a golden chandelier with cables threading up and down through the apparatus. These cables send precisely timed microwave pulses from room temperature down to the quantum realm, and relay information back out. The third layer consists of control electronics and sophisticated software—including QubiC, an open-source superconducting qubit control system developed by researchers in Berkeley Lab's Accelerator Technology & Applied Physics Division—that generates highly synchronized pulses to control the qubits and enable them to interact exactly as quantum computations require.
What makes the holistic approach essential is that any weak link in the stack can bottleneck the entire system. A quantum processor with exceptional coherence—meaning quantum information remains stable for long periods—becomes worthless if the microwave signals reaching it are noisy or degraded. Similarly, the wiring connecting to the dilution refrigerator represents a hidden constraint. Today's systems with a few dozen to a few hundred qubits use one or more wires per qubit. But as quantum computers scale upward, this architecture hits a wall. Fitting thousands of wires into a dilution refrigerator simply won't work. Researchers are actively investigating new low-noise wiring technologies to solve this scalability challenge while preserving quantum information lifetime.
The current quantum computers in operation represent what researchers call the intermediate scale—powerful enough to run interesting programs but not yet capable of outperforming classical supercomputers at meaningful tasks. Berkeley Lab is helping build the foundations for second-generation systems: large-scale, error-corrected quantum computers that will require thousands of qubits or far more. These systems will demand a complete integrated stack, with error correction built throughout.
"Making a functional quantum computer requires much more than qubits alone," Spitzer emphasizes. "It takes an entire technology stack that can harness quantum science for real-world applications." By partnering across industry, academia, and national laboratories, Berkeley Lab researchers are developing not individual components but an entire ecosystem—the infrastructure that transforms quantum potential into transformative science.