Quantum physics

While many quantum experiments examine very small objects, such as electrons and photons, quantum phenomena are all around us, acting on every scale. However, we may not be able to detect them easily in larger objects. This may give the wrong impression that quantum phenomena are bizarre or otherworldly. In fact, quantum science closes gaps in our knowledge of physics to give us a more complete picture of our everyday lives. Quantum discoveries have been incorporated into our foundational understanding of materials, chemistry, biology, and astronomy. These discoveries are a valuable resource for innovation, The Origins of Quantum Physics The field of quantum physics arose in the late 1800s and early 1900s from a series of experimental observations of atoms that didn't make intuitive sense in the context of classical physics. Among the basic discoveries was the realization that matter and energy can be thought of as discrete packets, or quanta, that have a minimum value associated with them. For example, light of a fixed frequency will deliver energy in quanta called "photons." Each photon at this frequency will have the same amount of energy, and this energy can't be broken down into smaller units. In fact, the word "quantum" has Latin roots and means "how much." Knowledge of quantum principles transformed our conceptualization of the atom, which consists of a nucleus surrounded by electrons. Early models depicted electrons as particles that orbited the nucleus, much like ...

quantum mechanics, The behaviour of matter and radiation on the atomic scale often seems peculiar, and the consequences of The study of quantum mechanics is rewarding for several reasons. First, it illustrates the essential Historical basis of quantum theory Basic considerations At a fundamental level, both radiation and matter have characteristics of

This is the first course in the undergraduate Quantum Physics sequence. It introduces the basic features of quantum mechanics. It covers the experimental basis of quantum physics, introduces wave mechanics, Schrödinger's equation in a single dimension, and Schrödinger's equation in three dimensions. The lectures and … Show more This is the first course in the undergraduate Quantum Physics sequence. It introduces the basic features of quantum mechanics. It covers the experimental basis of quantum physics, introduces wave mechanics, Schrödinger’s equation in a single dimension, and Schrödinger’s equation in three dimensions. The lectures and lecture notes for this course form the basis of Zwiebach’s textbook Mastering Quantum Mechanics published by This presentation of 8.04 by Barton Zwiebach (2016) differs somewhat and complements nicely the presentation of Show less

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Quantum physics articles from across Nature Portfolio • • Definition Quantum physics is the study of matter and energy at its most fundamental level. A central tenet of quantum physics is that energy comes in indivisible packets called quanta. Quanta behave very differently to macroscopic matter: particles can behave like waves, and waves behave as though they are particles. Featured • Future single-photon-based quantum networks will require both reliable telecom single-photon sources and improvements in security analysis. Here, the authors show how to use quantum dots and difference frequency generation to perform long-distance QKD, also reducing secure key acquisition time thanks to improved analytical bounds. • Christopher L. Morrison • Roberto G. Pousa • Alessandro Fedrizzi A deterministic single-photon two-qubit SWAP gate between polarization and spatial-momentum is demonstrated on a silicon chip. A two-qubit swapping process fidelity of 94.9% is obtained. The coherence preservation of the SWAP gate process is verified by two-photon interference. • Xiang Cheng • Kai-Chi Chang • Chee Wei Wong A common belief about boson bunching—fully indist...

For a demonstration that overturned the great Isaac Newton’s ideas about the nature of light, it was staggeringly simple. It “may be repeated with great ease, wherever the sun shines,” the English physicist Thomas Young told the members of the Royal Society in London in November 1803, describing what is now known as a But the birth of quantum physics in the early 1900s made it clear that light is made of tiny, indivisible units, or quanta, of energy, which we call photons. Young’s experiment, when done with single photons or even single particles of matter, such as electrons and neutrons, is a conundrum to behold, raising fundamental questions about the very nature of reality. Some have even used it to argue that the quantum world is influenced by human consciousness, giving our minds an agency and a place in the ontology of the universe. But does the simple experiment really make such a case? In the modern quantum form, Young’s experiment involves beaming individual particles of light or matter at two slits or openings cut into an otherwise opaque barrier. On the other side of the barrier is a screen that records the arrival of the particles (say, a photographic plate in the case of photons). Common sense leads us to expect that photons should go through one slit or the other and pile up behind each slit. They don’t. Rather, they go to certain parts of the screen and avoid others, creating alternating bands of light and dark. These so-called interference fringes, the kind...

But waves are inherently delocalised: they are ‘here’ and ‘there’. Einstein’s hypothesis didn’t overturn all the evidence for the delocalised wave-like properties of light. What he was suggesting is that a complete description somehow needs to take account of its localised, particle-like properties, too. In 1923, French physicist Louis de Broglie made a bold suggestion. If light waves can also be particles, could particles like electrons also be waves? This was just an idea, but he was able to use it to develop a direct mathematical relationship between an electron’s wave-like property (wavelength) and a particle-like property (momentum). Do particles really behave like waves? So, if electrons behave like waves, can they be diffracted? If we push a beam of electrons through two slits side-by-side will we see interference fringes on a distant screen? What if we limit the intensity of the beam so that, on average, only one electron passes through the slits at a time. What then? What we see is at first quite comforting. Each electron passing through the slits registers as a single spot on the screen, telling us that ‘an electron struck here’. This is perfectly consistent with notion of electrons as particles, as it seems they pass – one by one – through one or other of the slits and hit the screen in a seemingly random pattern. Interference patterns appearing in a double slit experiment But wait. The pattern isn’t random. As more and more electrons pass through the slits we c...

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Quantum physics articles from across Nature Portfolio • • Definition Quantum physics is the study of matter and energy at its most fundamental level. A central tenet of quantum physics is that energy comes in indivisible packets called quanta. Quanta behave very differently to macroscopic matter: particles can behave like waves, and waves behave as though they are particles. Featured • Future single-photon-based quantum networks will require both reliable telecom single-photon sources and improvements in security analysis. Here, the authors show how to use quantum dots and difference frequency generation to perform long-distance QKD, also reducing secure key acquisition time thanks to improved analytical bounds. • Christopher L. Morrison • Roberto G. Pousa • Alessandro Fedrizzi Quantum entanglement and uncertainty in the positions of light nuclei and implanted particles can crucially impact our understanding of advanced materials. This paper develops a unified theoretical description of these effects and applies it to muon spectroscopy measurements of a material constant to significantly improve their accuracy. • Matjaž Gomilšek • Francis L. Pra...

quantum mechanics, The behaviour of matter and radiation on the atomic scale often seems peculiar, and the consequences of The study of quantum mechanics is rewarding for several reasons. First, it illustrates the essential Historical basis of quantum theory Basic considerations At a fundamental level, both radiation and matter have characteristics of

But waves are inherently delocalised: they are ‘here’ and ‘there’. Einstein’s hypothesis didn’t overturn all the evidence for the delocalised wave-like properties of light. What he was suggesting is that a complete description somehow needs to take account of its localised, particle-like properties, too. In 1923, French physicist Louis de Broglie made a bold suggestion. If light waves can also be particles, could particles like electrons also be waves? This was just an idea, but he was able to use it to develop a direct mathematical relationship between an electron’s wave-like property (wavelength) and a particle-like property (momentum). Do particles really behave like waves? So, if electrons behave like waves, can they be diffracted? If we push a beam of electrons through two slits side-by-side will we see interference fringes on a distant screen? What if we limit the intensity of the beam so that, on average, only one electron passes through the slits at a time. What then? What we see is at first quite comforting. Each electron passing through the slits registers as a single spot on the screen, telling us that ‘an electron struck here’. This is perfectly consistent with notion of electrons as particles, as it seems they pass – one by one – through one or other of the slits and hit the screen in a seemingly random pattern. Interference patterns appearing in a double slit experiment But wait. The pattern isn’t random. As more and more electrons pass through the slits we c...

This is the first course in the undergraduate Quantum Physics sequence. It introduces the basic features of quantum mechanics. It covers the experimental basis of quantum physics, introduces wave mechanics, Schrödinger's equation in a single dimension, and Schrödinger's equation in three dimensions. The lectures and … Show more This is the first course in the undergraduate Quantum Physics sequence. It introduces the basic features of quantum mechanics. It covers the experimental basis of quantum physics, introduces wave mechanics, Schrödinger’s equation in a single dimension, and Schrödinger’s equation in three dimensions. The lectures and lecture notes for this course form the basis of Zwiebach’s textbook Mastering Quantum Mechanics published by This presentation of 8.04 by Barton Zwiebach (2016) differs somewhat and complements nicely the presentation of Show less