Caltech: Quantum Science and Technology

Quantum science grew out of studies of the smallest objects in nature. Today it promises to deepen our understanding of the universe and provide breakthrough technologies from quantum computers to ultra-precise measuring devices to next-generation materials, with many of these advances taking place at Caltech. Learn about the basic concepts of quantum science, including superposition, entanglement, and the principle of uncertainty. Discover how quantum principles and our understanding of them have been used to help society and catalyze new cross-disciplinary research.

If you are new to the field, we recommend starting here. Learn about the origins of quantum physics, also known as quantum mechanics, why mathematics is so important to this field, and how observing the smallest objects can affect it.

Find out how quantum computers work, the advances they make, and why universities, tech companies, and government agencies are racing to develop them.

Entanglement is at the heart of quantum physics and new quantum technologies. Read how scientists proved its existence and watch Caltech scientists explain this “creepy” phenomenon.

Go beyond Schrödinger’s cat and learn about superposition, a concept that may be difficult to visualize but could be the key to advancing technologies like quantum computers.

The uncertainty principle formulated in 1927 by the German physicist and Nobel Prize winner Werner Heisenberg states that we cannot know both the position and the speed of a particle such as a photon or electron with perfect accuracy. Find out why.

Let this comic take you into the laboratories where researchers explore the subatomic world of quantum physics.

Quantum information science has the potential to change computer encryption. Researchers envision secure cryptography that future quantum computers will not be able to crack and investigate how the properties of quantum mechanics could be used to send secure communications.

Surprising but true: quantum mechanics are at work in your toaster and other devices that we come across in everyday life.

Quantum computers aren’t the only application for quantum science. Caltech scientists are looking for ways to revolutionize chemistry, materials, sensing and more.

An atom is a tiny object, the basic unit of matter. It is made up of a nucleus made up of particles called protons and neutrons and one or more electrons, which are much lighter particles that surround the nucleus. Atoms play an important role in quantum science as quantum effects become visible at the atomic level.

Entanglement is a form of correlation between quantum particles. When two particles, such as a pair of photons or electrons, become entangled, they remain connected even if they are separated by great distances, and the state of one particle cannot generally be described without reference to the other.

NISQ stands for “Noisy Intermediate-Scale Quantum”, a term coined by John Preskill, Richard P. Feynman Professor of Theoretical Physics at Caltech, Allen VC Davis and Lenabelle Davis Leadership Chair and Director of the Institute for Quantum Information and Matter . The term is often used to describe the current state of quantum computing, in which processors contain a fraction of the qubits needed to tackle complex problems and yet interact with the environment in such a way that they lose some of their fragile quantum properties. Finding interesting uses for NISQ devices and going beyond the NISQ era are important research goals.

At its most basic level, all matter is made up of “fundamental particles” that don’t seem to break down into smaller units. These particles include quarks (which make up the protons and neutrons in the atomic nucleus) and electrons. Light also consists of particles, the so-called photons.

Quantum describes the rules and patterns of atomic and subatomic particles. Our experiences in daily life, which take place on a much larger scale, follow the rules of classical mechanics. But when we zoom in to examine the tiniest particles that make up the universe, we see strikingly different dynamics. Quantum science explains these phenomena to give us a deeper understanding of nature. The word “quantum” comes from the idea that physical properties like energy are not continuous but exist in specific – or quantized – amounts. A quant is the smallest possible unit of a physical property.

The term “Quantum Supremacy” was coined in 2012 by John Preskill, Richard P. Feynman Professor of Theoretical Physics at Caltech, Allen VC Davis and Lenabelle Davis Leadership Chair and Director of the Institute for Quantum Information and Matter to describe the point A quantum computer could perform tasks that would be impossible for a classical computer. More recently, many scientists and engineers have been using the term “quantum advantage” instead to describe the same benchmark.

Quantum encryption, also known as quantum cryptography, suggests using the laws of quantum physics, such as the uncertainty principle, to transmit private information in such a way that unnoticed eavesdropping becomes impossible.

A quantum internet would use the laws of quantum physics such as entanglement and superposition to send, receive and store information between networks of quantum devices much faster and more securely than is possible with the classical internet. A quantum internet would also enable the distribution of entanglement that could be used to perform quantum encryption, quantum sensing, and other quantum mechanical tasks. Although experiments continue to bring advances, a functioning quantum internet remains a distant goal.

Tiny particles are extremely sensitive to the environment. Scientists and engineers are trying to use this property, along with quantum principles such as entanglement, to develop instruments that can perform measurements with far greater precision than typical sensors such as seismometers, microscopes, or MRI machines. Many researchers consider quantum sensing as one of the next applications for quantum technology.

A quantum state is a mathematical representation of a quantum system that allows us to calculate certain observable properties of the system, such as its position or momentum. However, due to the uncertainty principle, these properties are not always determined, so that the resulting calculation usually yields a probability distribution (for example position X with a probability of 30 percent and position Y with a probability of 70 percent).

The basic unit of information in a classic computer is a bit. A bit is a binary digit that takes either the value 0 or 1. In contrast, the basic unit of quantum information is a qubit or quantum bit. A qubit can be in an overlap of 1 and 0 at the same time until its state is measured. In addition, the states of several qubits can be entangled, i.e. linked with one another quantum mechanically. Overlay and entanglement give quantum computers capabilities not available to their traditional counterparts.

Spin is an intrinsic property of tiny particles such as electrons, which is a quantum mechanical form of angular momentum (rotation).

The thought experiment proposed by physicist Erwin Schr̦dinger helps illustrate the concept of superposition, or the ability of a particle to exist in two states at the same time until it is measured. In the thought experiment, Schr̦dinger imagined putting a cat in a sealed box within an hour along with a poisonous substance that has an equal chance of killing the cat Рor not. He suggested that at the end of the lesson it could be said that the cat is both alive and dead, in a superimposition of states, until the box is opened and the act of observation determines its state to be alive or dead. With this example, Schr̦dinger wanted to show what he thought was the absurdity of quantum theory.

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