Power/Performance Bits: Nov. 9

Integrated transistor cooling; quantum error correction.


Integrated transistor cooling
Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) created a single chip that combines a transistor and microfluidic cooling system for more efficient transistor heat management.

The team focused on a co-design approach for the electrical and mechanical aspects of the chip, bringing the electronics and cooling design together and aiming to extract the heat very near the regions that heat up the most in the device.

“Managing the heat produced by these devices is one of the biggest challenges in electronics going forward,” said Professor Elison Matioli of EPFL’s School of Engineering’s Power and Wide-band-gap Electronics Research Laboratory. “It’s becoming increasingly important to minimize the environmental impact, so we need innovative cooling technologies that can efficiently process the large amounts of heat produced in a sustainable and cost-effective way.”

The microfluidic channels are inside the chip, allowing cooling liquid to flow through it. “We placed microfluidic channels very close to the transistor’s hot spots, with a straightforward and integrated fabrication process, so that we could extract the heat in exactly the right place and prevent it from spreading throughout the device,” said Matioli. In tests, the device was able to extract heat fluxes exceeding 1.7 kilowatts per square centimeter using only 0.57 watts per square centimeter of pumping power.

Fabricating the monolithically integrated manifold microchannel (mMMC) starts with etching narrow slits into a silicon substrate coated with gallium nitride (GaN) to create the channels. Isotropic gas etching is used to widen the slits in the silicon and connect short segments to create longer runs. The openings on the GaN layer are then sealed with copper, and the electronic device is fabricated in the GaN layer.

The cooling liquid they used was deionized water, which doesn’t conduct electricity. “We chose this liquid for our experiments, but we’re already testing other, more effective liquids so that we can extract even more heat out of the transistor,” said Remco Van Erp, a doctoral student at EPFL.

“This cooling technology will enable us to make electronic devices even more compact and could considerably reduce energy consumption around the world,” said Matioli. “We’ve eliminated the need for large external heat sinks and shown that it’s possible to create ultra-compact power converters in a single chip. This will prove useful as society becomes increasingly reliant on electronics.” The researchers are now looking at how to manage heat in other devices, such as lasers and communications systems.

Quantum error correction
Researchers from the University of Innsbruck, University of Bologna, and RWTH Aachen University developed a way to deal with errors and information loss in trapped-ion quantum computers.

Quantum computers can be subject to computational errors, such as bit flip or phase flip errors. However, the information-carrying qubits can also get lost entirely through actual loss of particles, such as atoms or ions, or due to quantum particles transitioning for instance to unwanted energy states. The loss of a qubit can have deleterious effects on the remaining qubits, leading to errors.

“Developing a fully functioning quantum processor still represents a great challenge for scientists across the world,” said Davide Vodola, a researcher at the University of Bologna. “This research allowed us, for the first time, to implement a protocol that can detect and, at the same time, correct errors due to qubit loss. This ability could prove to be essential for the future development of large-scale quantum computers.”

The team took a two-pronged approach to protecting against errors, starting with detecting the loss of qubits in the first place. “Measuring the qubit directly was not an option as this would destroy the quantum information that is stored in it,” explained Philipp Schindler from the University of Innsbruck.

Martin Ringbauer of the University of Innsbruck added, “We managed to overcome this problem by developing a technique where we used an additional ion to probe whether the qubit in question was still there or not, without disturbing it.”

The next step was adapting the rest of the computation in real-time in case the qubit was indeed lost, enabling quantum information to be unscrambled after a loss and maintain protection of the remaining qubits.

“To solve this problem, the first thing our research group did was to develop an effective theoretical approach to the issue,” said Vodola. “We managed to show that the information stored in a register with some qubits can be protected and fully retrieved in case one of these qubits gets lost.”

“We are happy with the results of this test on the trapped-ion quantum processor of the University of Innsbruck,” Vodola added. “The same protocol can be implemented in different quantum computer architectures that are currently under development by other research centers or private institutions.”

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