T-Systems Quantum Cloud customers now have access to AQT’s quantum computers, forming a partnership to strengthen Europe’s standing in ion trap-based quantum computing. AQT, based in Innsbruck and a prominent European player in this field, brings its quantum computers to T-Systems’ clients after successful integration tests.
Quantum computer power is still being stymied by numerous challenges. One such challenge is the requirement for each quantum bit to interact with all others.
Sensing with levitated nanoparticles has so far been limited by the precision of position measurements. Researchers at the Department of Experimental Physics of the University of Innsbruck, Austria, have now demonstrated a new technique that boosts the efficiency with which the position of a sub-micron levitated object is detected. The new technique demonstrated by Tracy Northup, a professor at the University of Innsbruck, and her team resolves this limitation by replacing the laser beam with the light of the particle reflected by a mirror.
At Innsbruck, Austria, a team of experimental physicists has now implemented a universal set of computational operations on fault-tolerant quantum bits for the first time, demonstrating how an algorithm can be programmed on a quantum computer so that errors do not spoil the result…
Physicists from Innsbruck, Austria, have now developed a method that enables optimization problems to be investigated on quantum hardware that already exists today.
The concept developed by the Innsbruck physicists to control dark states can in principle be implemented not only with superconducting quantum bits, but also on other technological platforms.
Quantum computers are advancing at a rapid pace and are already starting to push the limits of the world’s largest supercomputers. Yet, these devices are extremely sensitive to external influences and thus prone to errors which can change the result of the computation. This is particularly challenging for quantum computations that are beyond the reach of our trusted classical computers, where we can no longer independently verify the results through simulation. “In order to take full advantage of future quantum computers for critical calculations we need a way to ensure the output is correct, even if we cannot perform the calculation in question by other means,” says Chiara Greganti from the University of Vienna.
In a few years, a new generation of quantum simulators could provide insights that would not be possible using simulations on conventional supercomputers. Quantum simulators are capable of processing a great amount of information since they quantum mechanically superimpose an enormously large number of bit states. For this reason, however, it also proves difficult to read this information out of the quantum simulator. In order to be able to reconstruct the quantum state, a very large number of individual measurements are necessary. The method used to read out the quantum state of a quantum simulator is called quantum state tomography. “Each measurement provides a ‘cross-sectional image’ of the quantum state. You then put these cross-sectional images together to form the complete quantum state,” explains theoretical physicist Christian Kokail from Peter Zoller’s team at the Institute of Quantum Optics and Quantum Information at the Austrian Academy of Sciences and the Department of Experimental Physics at the University of Innsbruck. The number of measurements needed in the lab increases very rapidly with the size of the system. “The number of measurements grows exponentially with the number of qubits,” the physicist says. The Innsbruck researchers have now succeeded in developing a much more efficient method for quantum simulators.
Efficient method that delivers new insights
Insights from quantum field theory allow quantum state tomography to be much more efficient, i.e., to be performed with significantly fewer measurements. “The fascinating thing is that it was not at all clear from the outset that the predictions from quantum field theory could be applied to our quantum simulation experiments,” says theoretical physicist Rick van Bijnen. “Studying older scientific papers from this field happened to lead us down this track.” Quantum field theory provides the basic framework of the quantum state in the quantum simulator. Only a few measurements are then needed to fit the details into this basic framework. Based on this, the Innsbruck researchers have developed a measurement protocol by which tomography of the quantum state becomes possible with a drastically reduced number of measurements. At the same time, the new method allows new insights into the structure of the quantum state to be obtained. The physicists tested the new method with experimental data from an ion trap quantum simulator of the Innsbruck research group led by Rainer Blatt and Christian Roos. “In the process, we were now able to measure properties of the quantum state that were previously not observable in this quality,” Kokail recounts.
Verification of the result
A verification protocol developed by the group together with Andreas Elben and Benoit Vermersch two years ago can be used to check whether the structure of the quantum state actually matches the expectations from quantum field theory. “We can use further random measurements to check whether the basic framework for tomography that we developed based on the theory actually fits or is completely wrong,” explains Christian Kokail. The protocol raises a red flag if the framework does not fit. Of course, this would also be an interesting finding for the physicists, because it would possibly provide clues for the not yet fully understood relationship with quantum field theory. At the moment, the physicists around Peter Zoller are developing quantum protocols in which the basic framework of the quantum state is not stored on a classical computer, but is realized directly on the quantum simulator.
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The research was financially supported by the Austrian Science Fund FWF and the European Union, among others.
Publication: Entanglement Hamiltonian Tomography in Quantum Simulation. Christian Kokail, Rick van Bijnen, Andreas Elben, Benoit Vermersch, and Peter Zoller. Nature Physics 2021. doi: 10.1038/s41567-021-01260-w https://www.nature.com/articles/s41567-021-01260-w
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IMAGE: The compact quantum computer fits into two 19-inch server racks. View more. Image Credit: University of Innsbruck Over the past three decades, fundamental groundwork
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