What is quantum physics?
Quantum physics is the study of matter and energy at the most basic level, and its goal is to reveal the properties and behavior of the fundamental building blocks of nature.
While many quantum experiments focus on very, very small things, such as electrons and photons, quantum phenomena occur all around us and play a role at every scale. But it's not easy for us to spot them on larger objects. This gives the false impression that quantum phenomena are bizarre or "other world" things.
In fact, the advent of quantum science has filled the gap in our knowledge in the field of physics, giving us a more comprehensive understanding of the world in which we live.
The Origins of Quantum Physics
Born in the late 19th and early 20th centuries, quantum physics grew out of a series of experimental observations of atoms that simply did not make sense in the context of classical physics.
The most basic discovery in this field is that matter and energy can be thought of as discrete packets, or quanta. For example, light with some fixed frequency transmits energy in the form of quanta, that is, photons. Each photon at this frequency will have the same energy, and this energy cannot continue to be broken down into smaller units.
By the 20th century, this knowledge of quanta gradually changed our understanding of the microscopic world.
In the 1970s, physicists built the most accurate theory ever made, the Standard Model of particle physics, which explains the properties and behavior of all known elementary particles (such as electrons, photons, etc.) and their interactions.
The importance of mathematics
Many concepts of quantum physics are unimaginable to us, such as our inability to know exactly the position and velocity of a particle at the same time, or the fact that two entangled particles, no matter how far apart, can immediately obtain information about one of them once we know the other. To better understand these counterintuitive concepts, mathematics plays a crucial role. Equations are used to describe or help predict quantum objects and phenomena, which are much more precise than our imagination. Mathematics is also an indispensable tool for representing the probabilistic properties of quantum phenomena.
For example, early models described electrons as particles orbiting atomic nuclei, just as satellites orbit the Earth. But modern quantum physics suggests that the location of an electron may not be exact. Instead, it may be described as being in a series of possible locations (say, within a track), each with a probability of finding an electron there. When electrons gain or lose energy, they can "jump" from one orbit to another, but they do not appear in positions between orbits. Throughout the system, mathematics describes the probability that an electron exists in multiple locations at a particular range at any given time.
Given this nature of probability, quantum objects are often described in terms of the wave function in mathematics, the so-called solution to Schrödinger's equation. However, quantum objects can also be in multiple places at the same time, with different states, such as in the case of superposition. The solution to the wave function provides a possibility that the observer might find a particular object in a range of potential options.
Compared to other physical theories, quantum mechanics is special because it describes how objects can move like particles under certain conditions and like waves under other conditions. The core equation of quantum mechanics is the Schrödinger equation, which describes the change in time of the wave function ( ) , which is related to finding the probability distribution of a system in a particular state.
Experiments and observations
In experiments in quantum physics, observing (measuring) behavior is always an unavoidable topic. At the beginning of the development of this field, scientists were puzzled to find that mere observation alone would affect the results of experiments.
For example, an electron behaves like a wave when it is not observed, but the observed behavior causes the wave to collapse (the more accurate word is "decorrelation"), and the electron behaves like a particle. This variation in results may be caused by the interaction between quantum phenomena and the external environment, including the devices used for measurement.
A particle can be in a series of possible states, but when an observer makes a measurement, the wave function immediately collapses into a possible state.
Technical applications
The field of quantum science may seem mysterious and even illogical, but it does describe everything around us. The power of quantum physics has led to innovations in many technological applications. These discoveries are a valuable resource for innovation, giving birth to devices such as lasers, transistors, and even actual progress in technologies that were once considered pure speculation, such as quantum computers.
Currently, physicists are also exploring the potential of quantum science to change our understanding of gravity and its connection to space and time.
Appendix: Quantum-Related Technologies
Fluorescent lamps: The electrodes of fluorescent lamps heat up and shoot out electrons. These electrons in turn bombard small amounts of mercury inside the bulb. Collisions cause mercury's electrons to transition to a higher state of quantum energy. High-energy electrons tend to return to their originally lower-energy states, in the process in which photons are emitted, producing the light we see.
Semiconductors: As the name suggests, a semiconductor is a material with an electrical conductivity between conductors (such as copper) and insulators (such as glass), which are very useful in everyday electronics. In fact, the rise of all electronics is inseparable from our understanding of quantum mechanics. Conductivity can be thought of as the ability of electrons to share or delocalize between atoms in a material, which is the result of their quantum superposition.
Lasers: Lasers can emit concentrated beams of light because the directions of the light waves are all the same, and they are coherent, meaning they have the same frequency and waveform. The generation of lasers relies on the technique of stimulated emission, which uses a photon to stimulate an already excited atomic electron, causing it to descend to a lower quantum energy state and release two identical photons to propagate coherently. This process is repeated in a reflection chamber until many photons are emitted coherently together.
Magnetic resonance imaging: The amount of water and fat molecules stored in different organs and tissues in the human body varies, and the density of hydrogen atoms therefore varies. Magnetic resonance imaging (MRI) uses these differences to produce extremely detailed pictures. The positively charged protons of hydrogen atoms have a quantum spin associated with it, and the spin-on charged particles generate a magnetic field. Normally, the magnetic field of countless hydrogen atoms in the body points in different directions, but when a strong external magnetic field is applied, the axis of the atomic magnetic field is aligned. Subsequently, the instrument will apply a pulse of specially tuned radio frequencies, which will temporarily disrupt some hydrogen atoms again. Between pulses, the atoms are realigned with the external magnetic field. Throughout the process, regions of the body with more hydrogen atoms can be detected and distinguished.
Atomic Clocks: Typical clocks rely on quartz crystals to time them. When a voltage is applied, the crystal can vibrate at a precise frequency, and this vibration can be used to measure time, with an error in the range of one billionth of a second per hour. But in some technical applications, a more accurate clock is also needed. Atomic clocks are calibrated according to the microwave frequencies required to move electrons in atoms or ions from lower quantum energy states to higher quantum energy states. With this technique, the margin of error can be kept at no more than 1 second per 100 million years.
#创作团队:
Written by: M Ka
Design: Wenwen
#参考来源:
https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-physics
https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-technology
#图片来源:
Cover image: Pixabay
First image: https://shorts.quantumlah.org
Technology Applications: Joel Caswell for Caltech Science Exchange