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Scientists in Finland have developed a nanodevice that can measure the absolute power of microwave radiation down to the femtowatt level at ultra-low temperatures—a scale trillion times lower than routinely used in verifiable power measurements. The device has the potential to significantly advance microwave measurements in quantum technology.

Quantum science takes place mostly at ultra-low temperatures using devices called dilution refrigerators. The experiments also have to be done at tiny energy levels—down to the energy level of single photons or even less. Researchers have to measure these extremely low energy levels as accurately as possible, which means also accounting for heat—a persistent problem for quantum devices.

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If there are energy fluctuations in a quantum vacuum, very interesting things can happen. For example, the E = mc² relation tells us that energy and matter are interconvertible. A vacuum energy fluctuation can be converted into particles of matter. Sounds weird? Maybe, but it happens all the time. These particles are called virtual particles, living a fleeting existence before plunging back into the ever-busy quantum vacuum.

Tryon extrapolated the idea of quantum fluctuations to the Universe as a whole. He reasoned that if all that existed was a quantum vacuum, a bubble-like energy fluctuation out of this vacuum could have given rise to the Universe. Tryon proposed that the whole Universe is the result of a vacuum fluctuation, originating from what we could call quantum nothingness.

Magnetic materials with a triangular lattice have been the focus of numerous research studies, as theoretical predictions suggest that they could exhibit spin liquid states. These are quantum phases of matter that present interesting characteristics, such as quantum entanglement and fractionalized excitations.

While there have been numerous experimental efforts aimed at observing these fascinating phases in materials with a triangular lattice, this has so far proved to be very challenging. A key reason for this is that weak spin-orbit coupling and other perturbations in these materials typically result in conventional spin freezing or magnetic states.

Researchers at University of California, Boston College, Oak Ridge National Laboratory and the National Institute of Standards and Technology were recently able to produce a quantum disordered ground state in the triangular lattice-magnet NaRuO_2. Their findings, published in Nature Physics, suggest that this state was enabled by the cooperative interplay between spin-orbit coupling and correlation effects in the magnetic material.

A fluxonium qubit can keep its most useful quantum properties for about 1.48 milliseconds, drastically longer than similar qubits currently favoured by the quantum computing industry.

By Karmela Padavic-Callaghan

Scientists at EPFL have found a new way to create a crystalline structure called a “density wave” in an atomic gas. The findings can help us better understand the behavior of quantum matter, one of the most complex problems in physics. The research was published May 24 in Nature.

“Cold atomic gases were well known in the past for the ability to ‘program’ the interactions between atoms,” says Professor Jean-Philippe Brantut at EPFL. “Our experiment doubles this ability.” Working with the group of Professor Helmut Ritsch at the University of Innsbruck, they have made a breakthrough that can impact not only quantum research but quantum-based technologies in the future.

Scientists have long been interested in understanding how materials self-organize into complex structures, such as crystals. In the often-arcane world of quantum physics, this sort of self-organization of particles is seen in “density waves,” where particles arrange themselves into a regular, repeating pattern or order; like a group of people with different colored shirts on standing in a line but in a pattern where no two people with the same color shirt stand next to each other.

A quantum repeater based on trapped ions allows the transmission of entangled, telecom-wavelength photons over 50 km.

Communication networks have transformed our society over the past half century, and we can scarcely imagine our daily lives without them. Recent advances in the emergent field of quantum technologies have exhilarated scientists about the possibility of linking quantum devices in networks. Long-distance quantum communication portends functionality that is beyond the reach of classical networks [1]. To make full use of entanglement and other quantum effects, quantum networks exchange signals at the level of single photons. As a result, attenuation in fiber is the dominant source of error in these systems. Photon loss, however, can be remedied using a set of intermediate network nodes, called quantum repeaters, which create a direct entangled connection between distant network nodes [2].

Scalable photonic quantum computing architectures require photonic processing devices. Such platforms rely on low-loss, high-speed, reconfigurable circuits and near-deterministic resource state generators. In a new report now published in Science Advances, Patrik Sund and a research team at the center of hybrid quantum networks at the University of Copenhagen, and the University of Münster developed an integrated photonic platform with thin-film lithium niobate. The scientists integrated the platform with deterministic solid-state single photon sources using quantum dots in nanophotonic waveguides.

They processed the generated photons within low-loss circuits at speeds of several gigahertz and experimentally realized a variety of key photonic quantum information processing functionalities on high-speed circuits; with inherent key features to develop a four-mode universal photonic circuit. The results illustrate a promising direction in the development of scalable quantum technologies by merging integrated photonics with solid-state deterministic photon sources.

Quantum technologies have progressively advanced in the past several years to enable quantum hardware to compete with and surpass the capabilities of classical supercomputers. However, it is challenging to regulate quantum systems at scale for a variety of practical applications and also to form fault-tolerant quantum technologies.

A quarter century ago, theoretical physicists at the University of Innsbruck made the first proposal on how to transmit quantum information via quantum repeaters over long distances, which would open the door to the construction of a worldwide quantum information network.

Now, a new generation of Innsbruck researchers has built a quantum repeater node for the standard wavelength of telecommunication networks and transmitted quantum information over tens of kilometers. The study is published in the journal Physical Review Letters.

Quantum networks connect quantum processors or quantum sensors with each other. This allows tap-proof communication and high-performance distributed sensor networks. Between network nodes, quantum information is exchanged by photons that travel through optical waveguides. Over long distances, however, the likelihood of photons being lost increases dramatically.

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