As quantum computing systems scale toward thousands—if not millions—of qubits, the role of the often overlooked quantum amplifier that listens to each qubit becomes increasingly critical. Researchers in Sweden have reported that the development of a smarter, ultra-low-power quantum amplifier could significantly alleviate one of quantum computing‘s major engineering challenges.
Researchers in Sweden say they’ve engineered a smarter, ultra-low-power quantum amplifier that could dramatically ease one of quantum computing’s biggest engineering headaches.
A new study from Chalmers University of Technology, in collaboration with Low Noise Factory AB, unveils a cryogenic amplifier that switches on only when needed. This reduces energy consumption and thermal noise that threaten the fragile state of quantum bits or qubits.
The breakthrough, detailed in IEEE Transactions on Microwave Theory and Techniques, has the potential to pave the way for the realization of truly large-scale, fault-tolerant quantum computers, marking a significant advancement in the field.
“This is the most sensitive amplifier that can be built today using transistors,” lead author and doctoral student at Chalmers, Yin Zeng, said in the Chalmers press release. “We’ve now managed to reduce its power consumption to just one-tenth of that required by today’s best amplifiers – without compromising performance. We hope and believe that this breakthrough will enable more accurate readout of qubits in the future.”
Why Quantum Amplifiers Matter in Quantum Computers
At the core of quantum computing lies a fundamental difference from conventional computers. Unlike classical bits, which are limited to values of either 1 or 0, quantum bits—or qubits—can exist simultaneously in a state of both 1 and 0. This unique property, known as superposition, enables a quantum computer to represent many states at once, a capability that underpins its potential to solve complex problems.
For instance, a 20-qubit system can theoretically encode over a million combinations simultaneously. This exponential information capacity is what enables quantum computers to tackle problems that are impossible for even the most powerful classical supercomputers.
Quantum processors use extremely weak microwave signals to read a qubit’s state, which must be amplified before being processed. In superconducting systems, this task falls to high-electron-mobility transistor (HEMT) low-noise amplifiers (LNAs) that operate near absolute zero.
However, there’s a trade-off. As more qubits are added to a system, more quantum amplifiers are required—each contributing heat and noise. This scaling problem threatens to overwhelm cooling systems and jeopardize qubit fidelity.
To combat this, Zeng’s team took a novel approach, posing the question: What if you only turned on the amplifier when you were actually reading a qubit?
The Power of Pulsed Operation
The study introduces a novel “pulsed operation” mode for HEMT quantum amplifiers. Rather than operating continuously, the amplifier is activated only when a qubit’s state is read—a window typically lasting just hundreds of nanoseconds.
According to the team’s measurements, synchronizing the amplifier to this pulse minimizes its impact on the qubit and reduces average power consumption by up to nearly 86%.
This could make large-scale quantum systems more efficient and help eliminate bulky cryogenic components like isolators and circulators, which are traditionally used to block amplifier back-action from disturbing qubits.
Nevertheless, the idea isn’t as simple as just flipping a switch.
Qubits are highly sensitive, and any delay or noise introduced by turning the amplifier on and off could corrupt the measurement. To address this, the team modified a commercial HEMT amplifier—commonly used in quantum systems—to respond faster and cleaner.
Genetic Algorithms and Cryogenic Speed
One key innovation was optimizing how the quantum amplifier powers up. Instead of using a basic square waveform to toggle the quantum amplifier, the researchers developed a custom gate voltage waveform using a genetic algorithm (GA). This approach simulates evolution, testing thousands of waveform combinations to find one that produces the cleanest and fastest startup.
This resulted in a pulsed quantum amplifier that reaches full operating performance within just 35 nanoseconds—a fraction of typical qubit readout durations.
“This work presented pulsed operation of the cryogenic HEMT LNA aimed for qubit readout at very low-dc power in large-scale quantum computing systems,” researchers write. “We demonstrated that the LNA power dissipation can be significantly reduced without compromising critical performance by implementing pulsed operation.”
The team’s custom-built cryogenic testbed achieved 5-nanosecond resolution and noise fluctuation under 0.3 Kelvin, allowing them to precisely monitor the amplifier’s transient gain and noise behavior in real-time.
Real-World Impact on Quantum Amplifiers
When the optimized quantum amplifier was tested under realistic quantum operating conditions—with a readout pulse repeating every 5 microseconds—it consistently delivered stable, low-noise performance across cycles. More importantly, it cut average power consumption by more than 86%.
Multiply that level of energy efficiency across thousands of amplifiers in a quantum system, and the savings are dramatic—not only in electrical power but also in reduced cooling load and improved system reliability.
The work represents a crucial step toward scalable, modular quantum hardware that doesn’t require exotic refrigeration solutions or compromise qubit quality.
As noted in previous coverage of quantum developments by The Debrief—including a new magnetic material that could reduce susceptibility to environmental disturbances or IBM’s recent quantum simulation breakthrough—scaling up quantum computers will usher in an entirely new technological era. Reducing noise, improving fidelity, and managing thermal environments will be as critical as adding more qubits in new quantum systems.
The researchers see the potential for further improvements, including better power supply regulation and even more intelligent pulse shaping through advanced machine learning techniques. This ongoing research and development should inspire optimism about the future of quantum computing.
This new pulsed amplifier technique isn’t limited to superconducting qubits either. The researchers suggest that any quantum platform that relies on sensitive microwave readouts—such as spin qubits or photonic qubits—could benefit from similar strategies.
“This is the first demonstration of low-noise semiconductor amplifiers for quantum readout in pulsed operation that does not affect performance and with drastically reduced power consumption compared to the current state of the art,” co-author and professor of Microtechnology and Nanoscience, Dr. Jan Grahn, explained. “This study offers a solution in future upscaling of quantum computers where the heat generated by these qubit amplifiers poses a major limiting factor.”
As researchers conclude in their paper, “This advancement is crucial for reducing power dissipation and minimizing qubit disturbance, both being key factors for scalable quantum computing.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com