Quantum Dots: Applications for Artificial Atoms Expanding
By Lynn Savage, Feb 2011
Quantum dots, also known as semiconductor artificial atoms, have existed for several years now, and their use keeps on expanding. Primarily used as substitutes for dyes in fluorescence imaging, their propensity for being highly tunable emitters that resist photobleaching represents only a small fraction of their benefits.
Commonly but not always comprising cores of cadmium selenide with a coating of zinc sulfide, quantum dots are perhaps best known for the tunability of their emission wavelength, once excited by an external light source: Change the size of the particle, get a specific wavelength in return. Early research into the properties and potential uses for quantum dots kept them in solutions, and then later brought into proximity with a variety of other particles. This led to their nearly ubiquitous use as donors in Förster’s resonance energy transfer (FRET), a renowned method for near-diffraction-limit imaging of cells and other subjects. Continue reading
QUANTUM PHYSICS: THE PHYSICS OF DREAMING
By Paul Levy, 2014
6. SELF-EXCITED CIRCUIT
Wheeler’s vision of the universe is like a “self-excited circuit,” to use a metaphor from electronics. To say the universe is “self”-excited is to say it is not “other”-excited, which is to say that rather than depending upon an external agent, god or deity, the universe is self-creating and self-referential─i.e., able to refer to, reflect and act upon itself, and hence, endlessly re-create itself anew.
Seen as a self-excited and self-actualizing circuit, the physical universe bootstraps itself into existence, laws and all. As a self-excited circuit, the universe gives rise to observers who, in completing the circuit, potentially give meaningful reality to the universe. Wheeler says,
“The universe is to be compared to a circuit self-excited in this sense, that the universe gives birth to consciousness, and consciousness gives meaning to the universe.”
A SQUID (superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely subtle magnetic fields, based on superconducting loops containing Josephson junctions.
SQUIDs are sensitive enough to measure fields as low as 5 aT (5×10−18 T) within a few days of averaged measurements. Their noise levels are as low as 3 fT·Hz-½. For comparison, a typical refrigerator magnet produces 0.01 teslas (10−2 T), and some processes in animals produce very small magnetic fields between 10−9 T and 10−6 T. Recently invented SERF atomic magnetometers are potentially more sensitive and do not require cryogenic refrigeration but are orders of magnitude larger in size (~1 cm3) and must be operated in a near-zero magnetic field. Continue reading
Why Don’t Electrons Just Fall Into the Nucleus of an Atom?
By Esther Inglis-Arkell, 2014
Static electricity works because electrons are strongly attracted to protons, right? But, in atoms, electrons are right there, next to the protons in the nucleus. Why don’t the electrons zip directly into the nucleus and stick to the protons?
Everyone who has ever sat through fourth grade knows that when you rub a balloon on your hair, or your sweater, you can stick it to the wall. You can do this because the rubbing caused the balloon to accumulate a lot of electrons. Electrons are attracted to protons, and repelled by other electrons, so when the balloon was pushed near the wall, the electrons in the wall rushed away, leaving exposed Continue reading
Quantum teleportation is a process by which quantum information (e.g. the exact state of an atom or photon) can be transmitted from one location to another, with the help of classical communication and previously shared quantum entanglement between the sending and receiving location. Because it depends on classical communication, which can proceed no faster than the speed of light, it cannot be used for superluminal transport or communication of classical bits. It also cannot be used to make copies of a system, as this violates the no-cloning theorem.
Although the name is inspired by the teleportation commonly used in fiction, current technology provides no possibility of anything resembling the fictional form of teleportation. While it is possible to teleport one or more qubits of information between two (entangled) atoms, this has not yet been achieved Continue reading