Introduction
Quantum computers promise to revolutionize everything from cryptography to drug discovery, but their building blocks—qubits—are finicky. Superconducting qubits, prized for their tunability, must be kept at temperatures close to absolute zero to maintain their quantum states. Even then, errors creep in, and resetting a qubit to its pristine ground state is a daunting task. Traditional cooling methods, like dilution refrigerators, hit a wall around 50 millikelvin, leaving qubits with residual excitation that muddies computations.
The dream of fault-tolerant quantum computing hinges on one surprisingly difficult task: making a qubit forget. But what if forgetting didn’t need an operator—or even electricity? What if the laws of thermodynamics themselves could whisper the qubit back to zero?
The Old Conundrum
How do you cool something without spending extra energy or adding more noise to the system? For quantum technologies, that’s not a philosophical riddle—it’s a fundamental design problem. Why?
At the heart of every quantum processor lies a critical challenge: resetting qubits quickly and reliably. Qubits, unlike classical bits, are notoriously delicate. Any computational cycle must begin from a well-defined ground state. In today’s superconducting systems, that usually involves bulky cryogenic setups and active feedback control. But such techniques are resource-intensive and inherently limit how far we can scale.
The Bold Dream
Most of us have heard about—and at times, some of us, tried to picture—a quantum computer and its delicate qubits, teetering on the edge of chaos, where even a whisper of heat can scramble calculations. Now imagine a tiny, self-operating refrigerator that harnesses heat itself to cool these qubits to near-absolute zero, priming them for flawless computation. Far from science fiction, this represents a groundbreaking advancement in quantum engineering: a superconducting-circuit-based quantum absorption refrigerator capable of resetting qubits with unparalleled efficiency.
The Discovery
In a landmark achievement published in Nature Physics volume 21, pages 318–323 (2025), researchers at Aalto University and VTT Technical Research Centre of Finland have built a quantum refrigerator that resets a superconducting qubit using nothing but heat. The refrigerator operates autonomously, without control electronics or external feedback. It is minimal. It is beautiful. And it might change how we cool and control quantum computers in the future.
At the heart of the system is a delicate dance between three actors: a transmon qubit, a Josephson circuit acting as the refrigerator, and a resistor serving as a hot thermal bath. But unlike your kitchen fridge, this one doesn't hum with electricity—it ticks with entropy.
Here is where the research team from offers an alternative: let thermodynamics do the heavy lifting. Their experiment uses a simple but elegant setup: three superconducting circuits—two resonators and one transmon qubit—arranged in a V-shaped configuration. One resonator is hot (about 1 K), and the other cold (15 mK). When connected by a carefully tuned interaction, the energy flow from hot to cold drives the qubit back to its ground state—effectively “cooling” it through entropy exchange. This heat-powered operation mirrors the logic of classical absorption fridges, but here it’s implemented at the quantum scale, in a regime where quantum coherence and thermal noise are deeply entangled.
What makes the device remarkable isn’t just the result—it’s the autonomy. There’s no feedback loop, no active measurement. The system runs continuously and passively, with the thermal gradient acting as the control. The device resets the qubit at a speed of around 1.4 kHz and maintains a steady-state ground population of 80%. These numbers, while not yet outperforming conventional reset methods, are impressive for a proof-of-concept operating purely on heat.
But let’s step back. Why is qubit reset such a big deal?
The Reset Problem
Qubits, the fragile bits of quantum computers, are notorious for their tendency to remember. Before any computation can begin, a qubit must be reliably initialized in its ground state. Current quantum processors achieve this with active reset protocols, often involving fast pulses, feedback systems, or complex microwave control.
But these methods introduce heat and noise and require classical computation to oversee the operation—scaling them becomes increasingly complex as the number of qubits grows. Passive resets—where a qubit naturally relaxes to the ground state—take too long. An autonomous, fast, and scalable reset mechanism has long been sought.
This new thermal refrigerator delivers exactly that.
How It Works: A Thermodynamic Engine for Qubits
The experimental setup couples a transmon qubit (the target) to a specially designed Josephson circuit acting as the refrigerator. This "refrigerator qubit" is thermally biased: one of its electrodes is connected to a resistor held at a higher temperature (~200 mK), while the transmon remains near the base temperature (~25 mK) of the dilution refrigerator.
The architecture is a hybrid: a superconducting quantum circuit embedded with normal-metal elements. The thermal bias across the resistor injects energy into the refrigerator qubit, exciting it. This excited state can then be swapped with the transmon’s excited state via resonant exchange—essentially transferring entropy from the transmon into the hot bath. The process is autonomous and cyclic, driven by the flow of heat.
Over repeated cycles, the target qubit is pumped into its ground state with remarkable efficiency.
A Three-Body Dance
The magic happens through a carefully designed three-body interaction among the target qubit and the two qudits. This interaction allows the hot qudit to absorb energy from its bath, channeling it to pump heat out of the target qubit. The extracted heat flows into the cold qudit, which then dumps it into the cold bath. If the target qubit starts fully excited—its worst-case scenario—it settles into a steady state with an excited-state population of just 0.05%, equivalent to an effective temperature of about 22 millikelvin. This is a leap beyond traditional methods, which struggle to dip below 40–49 millikelvin, leaving qubits with 0.2 to 0.8% excitation.
Ground-State Fidelity: 92% and Rising
One of the striking outcomes is the fidelity of the reset. The refrigerator autonomously cools the transmon qubit to its ground state with a fidelity of 92%. This is achieved without external control pulses, fast switching, or even power consumption—just passive thermal gradients and smart circuit design.
The researchers show that this approach not only competes with active reset schemes in fidelity, but can surpass them in efficiency when scaled up. Moreover, the ground-state population is enhanced by nearly a factor of two compared to natural relaxation at base temperature.
And because the refrigerator is minimalistic and made using standard nanofabrication techniques, it is well-suited for integration into future quantum processors.
Implications: Toward Scalable, Self-Sufficient Quantum Chips
The implications of this work stretch far beyond just resetting qubits. By proving that thermodynamics alone can drive quantum state preparation, this experiment lays groundwork for future autonomous quantum systems—circuits that self-initialize, self-cool, and perhaps even self-correct.
Thermal logic, long a curiosity, may now find real hardware realization. Modular, scalable quantum architectures could rely on arrays of such thermal refrigerators, each servicing multiple qubits without adding thermal load or requiring complex routing.
Furthermore, the technique opens up deeper philosophical and practical questions about the intersection of quantum information and thermodynamic irreversibility. In a sense, this experiment turns heat—a traditional enemy of quantum coherence—into an ally.
The Immediate Scaling Up
While this refrigerator cools a single qubit, scaling it to handle multiple qubits in a quantum processor is the next frontier. Integrating it with larger circuits without adding heat load to the dilution refrigerator will require clever engineering, but the proof-of-concept shows promise. The ability to use existing temperature gradients in dilution refrigerators makes this approach adaptable to current quantum hardware.
A Glimpse into the Quantum Future
This work arrives at a crucial time. As quantum processors begin to scale from dozens to hundreds or even thousands of qubits, system-wide reliability becomes the bottleneck. Autonomous, low-energy, high-fidelity reset schemes are an essential piece of the puzzle.
By demonstrating a functioning quantum refrigerator that runs solely on heat, the researchers have rewritten one of the most overlooked chapters in the quantum computing playbook. They’ve shown that sometimes, to keep a quantum computer cool, all you need is a little heat.
Reference
Aamir, M.A., Jamet Suria, P., Marín Guzmán, J.A. et al. Thermally driven quantum refrigerator autonomously resets a superconducting qubit. Nat. Phys. 21, 318–323 (2025). https://doi.org/10.1038/s41567-024-02708-5