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A new class of quantum dots deliver a stable stream of single, spectrally tunable infrared photons under ambient conditions and at room temperature, unlike other single photon emitters. This breakthrough opens a range of practical applications, including quantum communication, quantum metrology, medical imaging and diagnostics, and clandestine labeling.

“The demonstration of high single-photon purity in the infrared has immediate utility in areas such as quantum key distribution for secure communication,” said Victor Klimov, lead author of a paper published today in Nature Nanotechnology by Los Alamos National Laboratory scientists.

The Los Alamos team has developed an elegant approach to synthesizing the colloidal-nanoparticle structures derived from their prior work on visible light emitters based on a core of cadmium selenide encased in a cadmium sulfide shell. By inserting a mercury sulfide interlayer at the core/shell interface, the team turned the quantum dots into highly efficient emitters of infrared light that can be tuned to a specific wavelength.

The torsion balance contains a rigid balance beam suspended by a fine thread as an ancient scientific instrument that continues to form a very sensitive force sensor to date. The force sensitivity is proportional to the lengths of the beam and thread and inversely proportional to the fourth power of the diameter of the thread; therefore, nanomaterials that support the torsion balances should be ideal building blocks. In a new report now published on Science Advances, Lin Cong and a research team in quantum physics, microelectronics and nanomaterials in China have detailed a torsional balance array on a chip with the highest sensitivity level. The team facilitated this by using a carbon nanotube as the thread and a monolayer graphene coated with aluminum films as the beam and mirror. Using the experimental setup, Cong et al. measured the femtonewton force exerted by a weak laser. The balances on the chip served as an ideal platform to investigate fundamental interactions up to zeptonewton in accuracy.

A modern role for ancient scientific instruments

The torsion pendulum is an ancient scientific instrument used to discover Coulomb’s law in 1785 and to determine the density of Earth in 1798. The instrument is useful across a range of applications including existing scientific explorations of precisely determining the gravitational constant. The most efficient method to achieve high sensitivity in the setup is by reducing the diameter of the suspension thread as much as possible. For instance, in 1931, Kappler et al. used a centimeters-long thread to develop a highly sensitive torsion balance to set a record for a hitherto unattained intrinsic force sensitivity. At present, carbon nanotubes form one of the strongest and thinnest materials known. In this work, the team synthesized ultra-long carbon nanotubes (CNTs) and large-area graphene to substantially increase the lengths of the balance beam and suspension thread to significantly improve the sensitivity of the instrument.

Bright semiconductor nanocrystals known as quantum dots give QLED TV screens their vibrant colors. But attempts to increase the intensity of that light generate heat instead, reducing the dots’ light-producing efficiency.

A new study explains why, and the results have broad implications for developing future quantum and photonics technologies where light replaces electrons in computers and fluids in refrigerators, for example.

In a QLED TV screen, dots absorb blue light and turn it into green or red. At the low energies where TV screens operate, this conversion of light from one color to another is virtually 100% efficient. But at the higher excitation energies required for brighter screens and other technologies, the efficiency drops off sharply. Researchers had theories about why this happens, but no one had ever observed it at the atomic scale until now.

The heart of any computer, its central processing unit, is built using semiconductor technology, which is capable of putting billions of transistors onto a single chip. Now, researchers from the group of Menno Veldhorst at QuTech, a collaboration between TU Delft and TNO, have shown that this technology can be used to build a two-dimensional array of qubits to function as a quantum processor. Their work, a crucial milestone for scalable quantum technology, was published today (March 242021) in Nature.

Quantum computers have the potential to solve problems that are impossible to address with classical computers. Whereas current quantum devices hold tens of qubits — the basic building block of quantum technology — a future universal quantum computer capable of running any quantum algorithm will likely consist of millions to billions of qubits. Quantum dot qubits hold the promise to be a scalable approach as they can be defined using standard semiconductor manufacturing techniques. Veldhorst: “By putting four such qubits in a two-by-two grid, demonstrating universal control over all qubits, and operating a quantum circuit that entangles all qubits, we have made an important step forward in realizing a scalable approach for quantum computation.”

Researchers at Chalmers University of Technology, Gothenburg, Sweden, have developed a novel type of thermometer that can simply and quickly measure temperatures during quantum calculations with extremely high accuracy. The breakthrough provides a benchmarking tool for quantum computing of great value—and opens up for experiments in the exciting field of quantum thermodynamics.

Key components in quantum computers are coaxial cables and waveguides—structures that guide waveforms and act as the vital connection between the quantum processor and the classical electronics that control it. Microwave pulses travel along the waveguides to the quantum processor, and are cooled down to extremely low temperatures along the way. The waveguide also attenuates and filters the pulses, enabling the extremely sensitive quantum computer to work with stable quantum states.

In order to maximize control over this mechanism, the researchers need to be sure that these waveguides are not carrying noise due to thermal motion of electrons on top of the pulses that they send. In other words, they have to measure the temperature of the electromagnetic fields at the cold end of the microwave waveguides, the point where the controlling pulses are delivered to the computer’s qubits. Working at the lowest possible temperature minimizes the risk of introducing errors in the qubits.

Big Blue has made Qiskit Metal generally available, to let “anyone” try their hand at quantum hardware design.

“Previously reported detection of plant biomagnetism, which established the existence of measurable magnetic activity in the plant kingdom, was carried out using superconducting-quantum-interference-device (SQUID) magnetometers1, 5, 16. Atomic magnetometers are arguably more attractive for biological applications, since, unlike SQUIDs34, 35, they are non-cryogenic and can be miniaturized to optimize spatial resolution of measured biological features14, 15, 36. In the future, the SNR of magnetic measurements in plants will benefit from optimizing the low-frequency stability and sensitivity of atomic magnetometers. Just as noninvasive magnetic techniques have become essential tools for medical diagnostics of the human brain and body, this noninvasive technique could also be useful in the future for crop-plant diagnostics—by measuring the electromagnetic response of plants facing such challenges as sudden temperature change, herbivore attack, and chemical exposure.”

Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electro-and magnetophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. Here we demonstrate that APs in a multicellular plant system produce measurable magnetic fields. Using atomic optically pumped magnetometers, biomagnetism associated with electrical activity in the carnivorous Venus flytrap, Dionaea muscipula, was recorded. Action potentials were induced by heat stimulation and detected both electrically and magnetically.

Pioneering experiment could help design energy-efficient materials.

In a groundbreaking study published in Physical Review Research, a group of University of Chicago scientists announced they were able to turn IBM’s largest quantum computer into a quantum material itself.

They programmed the computer such that it turned into a type of quantum material called an exciton condensate, which has only recently been shown to exist. Such condensates have been identified for their potential in future technology, because they can conduct energy with almost zero loss.