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A Quantum Bit

Quantum physics began with revolutionary discoveries in the early twentieth century and continues to be central in today’s physics research. Learn about quantum physics, bit by bit. From definitions to the latest research, this is your portal. Subscribe to receive regular emails from the quantum world.

September 15, 2016

From self-driving cars and IBM’s Watson to chess engines and AlphaGo, there is no shortage of news about machine learning, the field of artificial intelligence that studies how to make computers that can learn. Recently, parallel to these advances, scientists have started to ask how quantum devices and techniques might aid machine learning in the future.

To date, much research in the emerging field of quantum machine learning has attacked choke points in ordinary machine learning tasks, focusing, for example, on how to use quantum computers to speed up image recognition. But Vedran Dunjko and Hans Briegel at the University of Innsbruck, along with JQI Fellow Jake Taylor, have taken a broader view. Rather than focusing on speeding up subroutines for specific tasks, the researchers have introduced an approach to quantum machine learning that unifies much of the prior work and extends it to problems that received little attention before. They also showed how to increase learning performance for a large group of problems. The research has been accepted for publication in Physical Review Letters.

Quantum-enhanced machine learning. V. Dunjko, J. M. Taylor and H. J. Briegel, Physical Review Letters, to appear. arXiv:

September 6, 2016

Optical systems, like your eye, sometimes need help to produce a crystal clear image. And it’s not just a problem for eyes. Research labs, too, worry about aberrations and distortions that lead to image inaccuracies. JQI physicists have implemented a novel imaging technique that adapts to these destructive errors and corrects them. They combine high performance lenses, akin to an artificial eye, with computer processing to capture an image of a single atomic ion and its motion with unprecedented nanoscale sensitivity. The research is featured on the cover of the September issue of Nature Photonics.

High-resolution adaptive imaging of a single atom J. D. Wong-Campos, K. G. Johnson, B. Neyenhuis, J. Mizrahi & C. Monroe, Nature Photonics doi:10.1038/nphoton.2016.136

February 12, 2014

Atomtronics is an emerging technology whereby physicists use ensembles of atoms to build analogs to electronic circuit elements. Modern electronics relies on utilizing the charge properties of the electron. Using lasers and magnetic fields, atomic systems can be engineered to have behavior analogous to that of electrons, making them an exciting platform for studying and generating alternatives to charge-based electronics. Read more to learn more about recent atomtronics research.

February 4, 2014

Gretchen Campbell’s UMD laboratory has reached an important milestone in their experiment: a strontium Bose-Einstein condensate (BEC). This brings the total number of ultracold quantum gases at JQI to 10. These experiments study a rich variety of topics, from quantum information to many-body physics. Campbell's lab is the third in the world to condense strontium into a quantum state. Read more to learn more about these pristine quantum gases.

January 20, 2014

Quantum dots (QD) can be made from tiny crystals of semiconductor material, around 10 nanometers in size. The electron hole pairs in this structure are confined, resulting in a quantization of energy levels analogous to those of an atom – hence quantum dots are often dubbed ‘artificial atoms.’ Like an atom, a QD’s energy levels can be manipulated using lasers and magnetic fields. The fluorescing wavelengths can be tuned by altering the crystal size. Semiconductor quantum dots are attractive for quantum information processing because the technology for integration with modern electronics already exists. Read more to learn more about these artificial atoms.

January 8, 2014

An electron’s mass, charge, and magnetic moment are all measured to high precision. What about an electron’s electric dipole moment? Is it even there? An electric dipole moment (EDM for short) arises from a distortion in the distribution of electric charge. Some molecules like water, which consists of two hydrogen atoms and an oxygen atom, have nonzero EDMs because they have a bent, asymmetric shape. But the existence of an electron EDM has yet to be confirmed by experiment. In fact, it looks like the electron EDM is no larger than 0.000000000000000000000000000087 e-cm. Read more to learn more about why victory hasn't been declared.

December 13, 2013

Ring resonators are circular waveguides that are used as optical cavities. They look like tiny racetracks and are often fabricated from silicon. Photons can enter and exit a resonator and even move to neighboring waveguides through evanescent coupling. The micro-rings only let light waves circulate-- “resonate”-- if they have the right wavelength. This image, featured on the cover of the December 2013 issue of Nature Photonics, depicts an array of ring resonators designed to be a photonic analog to electrons experiencing quantum Hall physics. Read more to learn more about these micro-racetracks.

December 5, 2013

Vortices pop-up in the weather, sink drains, and even astrophysics; they also occur in superfluids, such as an ultracold atomic gas. The circulation in these systems obeys certain quantization criteria. When a superfluid is disturbed vortices will form in order to satisfy this circulation constraint. Vortices look like mini-tornados, having an essentially empty core or “eye." Stirring up a superfluid is one way to induce vortices. Introducing spin-orbit coupling can also do this. Another cool aspect: in seeking out the lowest energy configuration, the vortices will arrange into a lattice. Read more to learn more about core-less vortices—a quantum storm without an ‘eye.’

November 25, 2013

How long can a quantum superposition state survive? That length of time is called the coherence time, and depends on where a qubit lives. Quantum states are powerful for computing and exploring physics, but delicate when battling the environment. The key is to have a quantum state live longer than it takes to perform an operation or experiment. Physicists design complex containers that completely isolate quantum states from the surroundings. Read more to learn more about quantum coherence record holders.

November 18, 2013

Optical cavities can be made by arranging two mirrors facing each other. In this example, light bounces back and forth, forming a standing wave between the mirrors. One of the mirrors is designed to leak out a fraction of the light. Because of the boundaries created by the mirrors, the cavity will only build up light that satisfies a resonance condition--the light's wavelength must be a half-integer multiple of the cavity length. This means that cavities can be used to create narrow frequency sources. Read more to learn more about a cool research result using cavities.

November 14, 2013

Polarization refers to the orientation of traveling waves with respect to a well-defined direction. Polarized sunglasses shield your eyes from light having certain orientations. Projectors that display images having different polarizations are used to generate the 3D effects seen in movies. In quantum information research, two different polarization states of light can make up a photonic qubit.


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Quantum physics began with revolutionary discoveries in the early twentieth century and continues to be central in today’s physics research. Learn about quantum physics, bit by bit. From definitions to the latest research, this is your portal. Subscribe to receive regular emails from the quantum world. Previous Issues...

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