Research Highlights

Researchers at ETH have put a crystal into a quantum superposition state and measured for how long quantum effects in the vibrations of the crystal lasted. Such measurements are important for putting bounds on possible modifications of quantum theory that could explain why we do not see quantum features in everyday life.

Experimentalists at the Max Planck Institute of Quantum Optics in Garching (Germany), in close collaboration with theoretical physicist Eugene Demler at ETH Zurich, observed for the first time in microscopic detail how magnetic correlations mediate the pairing of quantum entities known as holes. The work establishes an intriguing platform for exploring theoretical models of high-temperature superconductivity — and might guide future efforts for designing novel quantum materials.

A method known as quantum key distribution has long held the promise of communication security unattainable in conventional cryptography. An international team of scientists, including ETH physicists, has now demonstrated experimentally, for the first time, an approach to quantum key distribution that uses high-quality quantum entanglement to provide much broader security guarantees than previous schemes.

ETH physicists have modified one of the major schemes for quantum error correction and put it into practice, demonstrating that they can substantially prolong the lifetime of quantum states — a crucial ingredient for future large-scale quantum computers.

In a material made of two thin crystal layers that are slightly twisted with respect to each other, researchers at ETH have studied the behaviour of strongly interacting electrons. Doing so, they found a number of surprising properties.

Physicists at ETH Zurich have demonstrated a five-metre-long microwave quantum link, the longest of its kind date. It can be used both for future quantum computer networks and for experiments in basic quantum physics research.

Physicists at ETH Zurich have observed a surprising twist in a quantum system caused by the interplay between energy dissipation and coherent quantum dynamics. To explain it, they found a concrete analogy to mechanics.

Quantum mechanics is a well-established theory, but at a macroscopic level it leads to intractable contradictions. Now ETH physicists are proposing to resolve the problem with the aid of neural networks.

In recent decades, NMR spectroscopy has made it possible to capture the spatial structure of chemical and biochemical molecules. Now researchers at ETH have found a way to apply this measurement principle to individual atoms.

In quantum physics the vacuum is not empty, but rather steeped in tiny fluctuations of the electromagnetic field. Until recently it was impossible to study those vacuum fluctuations directly. Researchers at ETH Zurich have developed a method that allows them to characterize the fluctuations in detail.

Researchers at ETH Zurich have used trapped calcium ions to demonstrate a new method for making quantum computers immune to errors. To do so, they created a periodic oscillatory state of an ion that circumvents the usual limits to measurement accuracy.

Light particles normally do not «feel» each other because there is no interaction acting between them. Researchers at ETH have now succeeded in manipulating photons inside a semiconductor material in such a way as to make them repel each other nevertheless.

The theory of quantum mechanics is well supported by experiments. Now, however, a thought experiment by ETH physicists yields unexpected contradictions. These findings raise some fundamental questions – and they’re polarising experts.

To make qubits for quantum computers less susceptible to noise, the spin of an electron or some other particle is preferentially used. Researchers at ETH Zurich have now developed a method that makes it possible to couple such a spin qubit strongly to microwave photons.

In the new quantum information technologies, fragile quantum states have to be transferred between distant quantum bits. Researchers at ETH have now realized such a quantum transmission between two solid-state qubits at the push of a button.

ETH physicists have developed a quantum cascade laser that can be used to visualise weak infrared signals from space. It is now being put to use on a flight of the world’s largest airborne observatory.

Nowadays, it is accepted among physicists that Albert Einstein was wrong in his scepticism of quantum mechanics. This was also confirmed by the Big Bell Test involving over 100,000 people around the world in November 2016.

Plants can convert sunlight into chemical energy with a high degree of efficiency. How this is achieved is still not entirely clear. ETH physicists have now constructed a quantum physical model that aims to answer this question.

An international collaboration led by ETH physicists has used machine learning to teach a computer how to predict the outcomes of quantum experiments. The results could prove to be essential for testing future quantum computers.

ETH physicists have developed a silicon wafer that behaves like a topological insulator when stimulated using ultrasound. They have thereby succeeded in turning an abstract theoretical concept into a macroscopic product.

When symmetries in quantum systems are spontaneously broken, the collective excitation modes change in characteristic ways. Researchers at ETH have now directly observed such Goldstone and Higgs modes for the first time.

Science and the IT industry have high hopes for quantum computing, but descriptions of possible applications tend to be vague. Researchers at ETH Zurich have now come up with a concrete example that demonstrates what quantum computers will actually be able to achieve in the future.

Accurate measurements of the frequencies of weak electric or magnetic fields are important in many applications. Researchers at ETH Zurich have now developed a procedure whereby a quantum sensor measures the frequency of an oscillating magnetic field with unprecedented accuracy.

Gases in the environment can be spectroscopically probed fast and precisely using so-called dual frequency combs. Researchers at ETH have now developed a method by which such frequency combs can be created much more simply and cheaply than before.

Light particles do not usually react to magnetic fields. Researchers at ETH Zurich have now shown how photons can still be influenced by electric and magnetic fields. In the future that method could be used to create strong artificial magnetic fields for photons.

When matter is cooled to near absolute zero, intriguing phenomena emerge. These include supersolidity, where crystalline structure and frictionless flow occur together. ETH researchers have succeeded in realising this strange state experimentally for the first time.

Theoretical physicists from ETH Zurich deliberately misled intelligent machines, and thus refined the process of machine learning. They created a new method that allows computers to categorise data – even when humans have no idea what this categorisation might look like.

Quantum systems consisting of many particles are a major challenge for physicists, since their behaviour can be determined only with immense computational power. ETH physicists have now discovered an elegant way to simplify the problem.

Quantum mechanics can be entertaining: anyone with a few minutes to spare for a video game on 30 November can do their bit to help solve a fundamental question of physics that was once argued over by Albert Einstein and Nils Bohr. ETH Professor Andreas Wallraff explains what the Big Bell Test is all about.

Electrons in a solid can team up to form so-called quasiparticles, which lead to new phenomena. Physicists at ETH in Zurich have now studied previously unidentified quasiparticles in a new class of atomically thin semiconductors. The researchers use their results to correct a prevailing misinterpretation.

The electronic energy states allowed by quantum mechanics determine whether a solid is an insulator or whether it conducts electric current as a metal. Researchers at ETH have now theoretically predicted a novel material whose energy states exhibit a hitherto unknown peculiarity.

For years physicists have strived to control the quantum states of atoms or molecules very accurately. Researchers at ETH Zurich have now established a record for the size of  quantum states generated with massive particles. Their technique could be used to make quantum computers faster.

Well-controlled shuttling of ions through laser beams should enable scalable quantum computing.

In phase transitions, for instance between water and water vapour, the motional energy competes with the attractive energy between neighbouring molecules. Physicists at ETH Zurich have now studied quantum phase transitions in which distant particles also influence one another.

Entanglement between distant quantum objects is an important ingredient for future information technologies. Researchers at the ETH have now developed a method with which such states can be created a thousand times faster than before.

Studying peculiar properties of a long known metallic material researchers have chanced upon a new particle. It is related to the so-called Weyl fermions that the mathematician Hermann Weyl predicted almost ninety years ago. Weyl had overlooked the particle, which could have interesting applications in electronics.

Resonators are an important tool in physics. The curved mirrors inside the resonators usually focus light waves that act, for instance, on atoms. Physicists at ETH Zurich have now managed to build a resonator for electrons and to direct the standing waves thus created onto an artificial atom.

Sebastian Huber and his colleagues show that the road from abstract theory to practical applications needn’t always be very long. Their mechanical implementation of a quantum mechanical phenomenon could soon be used for soundproofing purposes.

Jonathan Home’s laboratory has a room full of equipment that traps tiny ions and places them in special quantum states – perhaps the first step towards building a quantum computer.

In experiments using ultracold atoms and laser light, ETH researchers have measured a stepwise change in conductivity as the atoms pass through tiny structures. This is the first time that this quantum effect has been observed for electrically neutral particles.

Google and American defence company Lockheed Martin paid more than USD 10 million for a quantum computer, although its exact capabilities are unknown. A team headed by ETH professor Matthias Troyer examined the question of how to properly test such devices, creating quite a stir in the process.

A new and innovative computing machine is currently attracting a great deal of attention in specialist circles. A team under the leadership of Matthias Troyer, a professor at ETH Zurich, has now confirmed that the machine uses quantum effects. However, it is not any faster than a traditional computer.