Precise spectroscopy of a simple molecular ion opens a new path toward stringent tests of quantum electrodynamics.
Category: quantum physics
Optical control of nuclear spins in molecules points to new paths for quantum technologies
Researchers at the Karlsruhe Institute of Technology (KIT) have reported important progress in quantum physics and materials science by optically initializing, controlling, and reading out nuclear spin states in a molecular material for the first time. Because of their weak interaction with the environment, nuclear spins are particularly stable quantum information carriers. The research, published in Nature Materials, shows that molecular nuclear spins could be a promising building block for future quantum technologies.
Nuclear magnetic resonance (NMR) is an established method for analyzing materials and molecules, with applications ranging from chemical analysis to quantum information processing. For a new paper, KIT researchers analyzed a molecular crystal containing europium ions. Such ions have especially narrow optical transitions that allow direct addressing of nuclear spin states. Using laser light, they were able to initialize nuclear spins in defined states and then read out those states.
In addition to optical addressing, the researchers used high-frequency fields to control the spins and protect them from interfering environmental influences. They achieved nuclear spin quantum coherence with a lifetime of up to two milliseconds, an interval during which a quantum system maintains a precisely defined quantum mechanical state.
Robust against noise, geometric-phase swap gates bring stability to quantum operations
Researchers at ETH Zurich have realized particularly stable quantum logical operations with qubits made of neutral atoms. Since these operations, called quantum gates, are based on geometric phases, they are extremely robust against experimental noise and can be used in quantum computers in the future.
Quantum bits, or qubits, which are required for building quantum computers, come in different kinds. In recent years, many research institutes and companies have focused on superconducting circuits and trapped ions. However, neutral atoms trapped with laser light also have a lot going for them: since they carry no electric charge, they are less sensitive to disturbances. Moreover, trapping with laser light makes it easy to realize several thousand qubits in a single system—using superconductors or ions this is much more difficult.
Nevertheless, neutral atoms have their own problems. In quantum computers, qubits exist in superposition states of the logic values 0 and 1. To perform calculations with them, one needs to execute quantum logic operations, also known as quantum gates.
Electron–atom scattering encodes the quantum state of electron wave packets
A new analysis reveals what happens when very short or narrow electron beams encounter a particle. The research is published in the New Journal of Physics. Scientists should be able to achieve a new level of control over high-energy electrons interacting with a particle, according to the theoretical analysis by a RIKEN physicist and two colleagues.
Electrons are particles, but according to quantum mechanics they also behave like waves under certain circumstances.
Electron microscopes exploit this wave-like nature of electrons to obtain high-resolution images of objects by imaging how an electron beam is scattered from an object.
Giant Atoms for Measuring Radiation
The invention of the radio just over a century ago transformed people’s ability to communicate. Suddenly, people could send and receive light-speed messages from thousands of miles away — a capability that continues to transform the world.
Soon, quantum scientists could usher in the next big advance in radio communication: compact, highly sensitive receivers based on atoms.
Atoms are typically far too small to interact with radio waves. But one of quantum theory’s stranger predictions is the possibility of gargantuan atoms with diameters up to the width of a human hair.
How a century-long argument over light’s true nature came to an end
Two of the forefathers of quantum theory, Albert Einstein and Niels Bohr, had a famous argument over whether light is a wave or a particle. Columnist Karmela Padavic-Callaghan finds that the matter has been settled once and for all.
Quantum computing without interruptions
Mid-circuit measurements are one of the biggest practical hurdles in quantum error correction on encoded qubits. Researchers in Innsbruck and Aachen have now proposed and experimentally demonstrated that a universal fault-tolerant quantum algorithm can be executed without such measurements. Using a trapped-ion quantum processor, the team successfully ran Grover’s quantum search algorithm on three logical qubits.
A key bottleneck in today’s leading approaches to quantum error correction is the need to repeatedly pause and measure the quantum processor mid-computation, a process that is slow, technically demanding, and itself a significant source of errors.
Now, a joint team from the University of Innsbruck, RWTH Aachen University, Forschungszentrum Jülich and spin-off Alpine Quantum Technologies (AQT) has demonstrated fault-tolerant quantum computation without any such interruptions.
Mechanical inputs boost diamond quantum sensor states as Q factor tops one million
Most people think of diamonds as high-end adornments. Not Ania Bleszynski Jayich. The UC Santa Barbara physicist sees diamonds, which she grows in the UC Quantum Foundry, as a potentially powerful foundation for quantum sensors. Sensors are currently much farther along in their development than other potential quantum applications. Diamond sensors are particularly promising because diamonds require relatively few quantum bits (qubits) to operate, whereas a quantum computer, for instance, requires more than 100,000, perhaps as many as a million, qubits to handle error correction, one of the main hurdles for quantum computing.
A paper about the latest advance from the Bleszynski Jayich lab, “Spin-embedded diamond optomechanical resonator with a mechanical quality factor exceeding one million,” has been published in the journal Optica.
Quantum ground state of rotation achieved for the first time in two dimensions
Quantum mechanics tells us that a particle can never be perfectly still. But how precisely can it be oriented? A research team at the University of Vienna, together with colleagues at TU Wien and Ulm University, has now cooled the rotational motion of a levitated silica nanorotor all the way to its quantum ground state—in two orientational degrees of freedom.
Reporting in Nature Physics, they show how optical cooling confines the nanoparticle’s orientation to within the bounds of quantum zero-point fluctuations, the unavoidable orientational uncertainty imposed by Heisenberg’s uncertainty principle. Such quantum-limited alignment is an important milestone towards rotational matter-wave interferometry and ultra-sensitive quantum torque sensing.