What is entanglement in quantum physics? We'll explain in under 5 minutes

Quantum, quantum mechanics, The law of conservation of energy

, , and are often in the news these days. Articles about them inevitably refer to entanglement, a property of quantum physics that makes all these magical devices possible.

Einstein called entanglement “,” a name that has stuck and become . Beyond just building better , understanding and harnessing entanglement is also useful in other ways.

For example, it can be used to make more accurate measurements of , and to better understand the properties of . It also subtly shows up in other places: I have been studying how atoms bumping into each other become entangled, to understand how this affects the accuracy of atomic clocks.

But what is entanglement? Is there some way to understand this “spooky” phenomenon? I will try to explain it by bringing together two notions from physics: conservation laws and quantum superpositions.

Conservation laws

are some of the deepest and most pervasive concepts in all of physics. The law of conservation of energy states that the total amount of energy in an isolated system remains fixed (although it can be converted from electrical energy to mechanical energy to heat, and so on). This law underlies the workings of all of our machines, whether they are steam engines or electric cars. Conservation laws are a kind of accounting statement: you can exchange bits of energy around, but the total amount has to stay the same.

(momentum being mass times velocity) is the reason why, when two ice skaters with different masses push off from each other, the lighter one moves away faster than the heavier. This law also underlies the famous dictum that “every action has an equal and opposite reaction.” Conservation of angular momentum is why — going back to ice skaters again — a whirling by drawing her arms closer to her body.

Quantum, quantum mechanics, The law of conservation of energy
France’s Gabriella Papadakis and Guillaume Cizeron demonstrate the effects of conservation laws during the 2019 ISU European Figure Skating Championships in Belarus.

These conservation laws have been experimentally verified to work across an extraordinary range of scales in the universe, from all the way down to the tiniest .

Quantum addition

Picture yourself on a nice hike through the woods. You come to a fork in the trail, but you find yourself struggling to decide whether to go left or right. The path to the left looks dark and gloomy but is reputed to lead to some nice views, while the one to the right looks sunny but steep. You finally decide to go right, . In a quantum world, you could have chosen both.

For systems described by quantum mechanics (that is, things that are sufficiently well isolated from heat and external disturbances), the rules are more interesting. Like a spinning top, an electron for example can be in a state where it spins clockwise, or in another state where it spins anticlockwise. Unlike a spinning top though, it can also be in a state that is [clockwise spinning] + [anticlockwise spinning].

The states of quantum systems can be added together and subtracted from each other. Mathematically, the rules for combining quantum states can be described in the same way as the rules for . The word for such a combination of quantum states is a superposition. This is really what is behind strange quantum effects that you may have heard about, such as the double-slit experiment, or particle-wave duality.

Say you decide to force an electron in the [clockwise spinning] + [anticlockwise spinning] superposition state to yield a definite answer. Then the electron randomly ends up either in the [clockwise spinning] state or in the [anticlockwise spinning] state. The odds of one outcome versus the other are easy to calculate (with a at hand). The intrinsic randomness of this process may bother you if your worldview requires the universe to behave in a way, but … c’est la (experimentally tested) vie.

Conservation laws and quantum mechanics

Let’s put these two ideas together now, and apply the law of conservation of energy to a pair of quantum particles.

Imagine a pair of quantum particles (say atoms) that start off with a total of 100 units of energy. You and your friend separate the pair, taking one each. You find that yours has 40 units of energy. Using the law of conservation of energy, you deduce that the one your friend has must have 60 units of energy. As soon as you know the energy of your atom, you immediately also know the energy of your friend’s atom. You would know this even if your friend never revealed any information to you. And you would know this even if your friend was off on the other side of the galaxy at the time you measured the energy of your atom. Nothing spooky about it (once you realize this is just correlation, not causation).

But the quantum states of a pair of atoms can be more interesting. The energy of the pair can be partitioned in many possible ways (consistent with energy conservation, of course). The combined state of the pair of atoms can be in a superposition, for example:

[your atom: 60 units; friend’s atom: 40 units] + [your atom: 70 units; friend’s atom: 30 units].

This is an entangled state of the two atoms. Neither your atom, nor your friend’s, has a definite energy in this superposition. Nevertheless, the properties of the two atoms are correlated because of conservation of energy: their energies always add up to 100 units.

For example, if you measure your atom and find it in a state with 70 units of energy, you can be certain that your friend’s atom has 30 units of energy. You would know this even if your friend never revealed any information to you. And thanks to energy conservation, you would know this even if your friend was off on the other side of the galaxy.

Nothing spooky about it.

This article by , Assistant Professor of Physics, is republished from under a Creative Commons license. Read the .

News Related

OTHER NEWS

Samsung Galaxy S22 screen and battery could both be smaller than the S21

We’ve seen the iPhone 13 now, so what does the Samsung Galaxy S22 have to offer? A screen size and battery capacity that are both smaller than what we currently ... Read more »

The Tech Weekender: Top news from the world of technology this week

Apple had a major week with the launch of the new iPhone 13 series. The iPhone 13, iPhone 13 mini, iPhone 13 Pro, and iPhone 13 Pro Max arrive with ... Read more »

Donald Trump gave his adult children 6 months of Secret Service protection after he left office, at the taxpayers' expense, says report

Former president Donald Trump with his family. Fred Watkins/Getty Images Donald Trump gave his adult children and three officials six months extra Secret Service protection. The extra security cost taxpayers ... Read more »

Giant fish takes down shark in incredible video

Giant fish takes down shark in incredible video Read more »

7 ways men live without working in America

SAN FRANCISCO, CALIFORNIA – SEPTEMBER 16: A pedestrian walks by a help wanted sign posted in the window of hardware store on September 16, 2021 in San Francisco, California. Unemployment ... Read more »

Save big on TVs and more with Best Buy's Ultimate Home Theatre Sale

Looking for more of the best deals, sales and product recommendations? Sign up for Yahoo Lifestyle Canada’s newsletter! Best Buy is slashing prices on smart TVs, audio equipment and TV ... Read more »

This Samsung tablet is the first real alternative to the iPad—and it's on sale

We may receive commission from purchases made via links on this page. Pricing and availability are subject to change. Score this Samsung Galaxy Tab A (8-inch) on sale. (Photo: Samsung) ... Read more »

Top Gaming Chair 2021 | Our Top Pick!

Welcome back to The Ultimate Tech Hub. On today’s episode we are reviewing the FUQIDO 6627 Gaming Chair. This Premium Gaming Chair is designed for Big & Tall people. This ... Read more »

6 buggy examples of Tesla's Full Self-Driving software that show why drivers have to be ready to take over on a second's notice

Reuters Tesla rolled out version 10 of its Full Self-Driving software earlier this month. Since, videos of the FSD update have shown several instances when the car has acted wonky. ... Read more »

Don't try this with your new iPhone: 6 hot tips to shooting with ‘action cams'

Even with all the hype surrounding Apple’s new iPhone 13 family and its improved cameras, a recent Apple Support blog post reminds users that exposure to vibrations, caused by improperly ... Read more »

Surface Go 3 leaked spec suggests a big improvement in battery life

The Surface Go 3, the next-gen tablet which is purportedly set to be revealed early next week at Microsoft’s Surface press event – potentially among many other goodies – has ... Read more »

Samsung Galaxy S21 FE support page goes live in Germany, hinting towards imminent launch

Samsung Galaxy S21 FE launch is rumoured for October 2021 (Image: OnLeaks) Samsung’s last Galaxy Unpacked event saw the unveiling of its much-anticipated foldable phones, but the unveiling of the ... Read more »

Fears for listed landmarks as Nadine Dorries lets the wrecking ball swing

Nadine Dorries’s decision to change the status of the Dorman Long Tower, right, has paved the way for the landmark to be destroyed – Getty Images/PA Nadine Dorries, the new ... Read more »

Why Sir Clive Sinclair never quite became the British Steve Jobs

Sir Clive with the much-derided Sinclair C5 – Hulton Archive Sir Clive Sinclair, the British electronics entrepreneur and father of the home computer who died this week, aged 81, could ... Read more »

Leslie Ash was told by doctors she'd need a wheelchair by the age of 60

Leslie Ash has defied medical predictions and avoided having to use a wheelchair to get around. (David M. Benett/Getty Images) Leslie Ash has revealed she has defied the predictions of ... Read more »

Aussies react to French backlash over submarine deal

“It’s a stab in the back. We created a relationship of trust with Australia and that trust has been broken,” French Foreign Minister Jean-Yves Le Drian said on Thursday. However, ... Read more »

Great British Bake Off's first vegan contestant faces online backlash – for riding horses

Freya Cox The Great British Bake Off’s first vegan contestant has been forced off Facebook after being called a hypocrite for riding horses. Freya Cox, 19, was targeted by social ... Read more »

Shirley Ballas says she likes 'Horlicks and sex' before going to bed at night

Shirley Ballas says her sex life is still hugely important to her at the age of 61. (David M. Benett/Getty Images) Strictly Come Dancing head judge Shirley Ballas has revealed ... Read more »

Beer, fizzy drinks and meat supplies threatened as CO2 shortage deepens

British supermarkets have been facing supply shortages all summer before this latest issue (Getty Images) The UK is bracing itself for a severe shortage of CO2 gas impacting supplies of ... Read more »

UK's first shared e-cargo bike scheme launches in London

This article was originally published by  on , the leading news platform on urban mobility and innovation, reaching an international audience of city leaders. For the latest updates, follow Cities Today on , , , , ... Read more »

Motorola tablet expected to launch during Flipkart's Big Billion Days Sale

Motorola is gearing up to launch a new tablet in India during Flipkart’s Big Billion Days Sale. This will be Motorola‘s first tablet launch in the country since Motorola Xoom or ... Read more »

Xiaomi patents earthquake monitoring mobile tech

Beijing, Chinese tech giant Xiaomi has published a patent for ‘Method and Equipment for Realizing Seismic Monitoring of Mobile Devices’ with publication number CN113406696A.The patent describes a system that is ... Read more »

Two spacetech startups get access to Isro facilities, expertise to test rocket systems

The department of space entered into a similar MoU with Hyderabad-based Skyroot Aerospace last week for access to Isro facilities and expertise towards the development and testing of subsystems/systems of ... Read more »

Airtel chief's comments on floor price validate Trai stance: Official

NEW DELHI: Bharti Airtel chairman Sunil Bharti Mittal’s comments that the industry does not need regulatory intervention for pricing has validated the telecom regulator’s stance that setting up floor tariffs ... Read more »

Big Tech grapples with Russian internet crackdown during election

Big Tech companies’ human rights policies have been stress-tested in the run-up to Russian parliamentary elections, as the Kremlin cracks down on a broad range of content. Read more »

Amazon just took 40 percent off these wireless earbuds — snag them for just $24

We may receive commission from purchases made via links on this page. Pricing and availability are subject to change. Just 24 bucks for a pair of excellent earbuds? Done(rton), and ... Read more »

Samsung QN900A Neo QLED 8K TV UAE

© Provided by TechRadar Samsung QN900A Neo QLED 8K One-minute review On the cusp of a new era in TV technology, Samsung’s Mini LED-sporting QN900A Neo QLED 8K TV offers ... Read more »

Gogglebox Issues Response After Paige Deville Announces Exit With Statement Blasting Show

Gogglebox bosses have issued a response after star Paige Deville quit the show and made a number of accusations about it. On Friday, Paige – who appeared alongside her mum ... Read more »

SpaceX Inspiration4 mission: Crew appear in live video featuring somersaults and a ukulele performance

The first all-civilian astronaut crew to reach orbit have appeared in a live video feed featuring weightless flips and a ukulele performance. SpaceX has announced that the crew are expected to return to Earth on Saturday, just after 11pm GMT. Read more »

Veil of secrecy at Apple cannot hide worker unrest

A common theme is that Apple’s secrecy has created a culture that discourages employees from speaking out about their workplace concerns — not with co-workers, not with the press and ... Read more »

Canon EOS R3 vs Canon EOS R5: 9 key differences between the mirrorless beasts

In a year when we’ve been treated to a wave of high-end cameras, we’ve been waiting for Canon’s full reveal of its hotly-anticipated EOS R3 since the development announcement back ... Read more »

iPhone 14 early leaks, news and what we know so far

The iPhone 13 has only recently been unveiled but already we’ve heard quite a lot about the iPhone 14, Apple’s flagship phone expected in late 2022, with leakers revealing possible ... Read more »

Council worker 'smashed car window with lawnmower then tried to cover it up'

A council worker has been accused of smashing a car window with a lawnmower then trying to cover it up. Jay Elton, 31, from Willerby, East Yorkshire, said his local ... Read more »

Dog that killed boy in Cornwall had attacked before, inquest hears

A coroner is to write to a police force about a nine-year-old boy who was mauled to death by a dog during a Cornish holiday, after his inquest heard the ... Read more »

'Celebrity MasterChef' 2021: And the winner is...

Kadeena Cox, Joe Swash and Megan McKenna were in the final. (Shine TV) Kadeena Cox has been named as the winner of Celebrity MasterChef 2021. Paralympic athlete Cox fought off ... Read more »

What the hell is that weird flashing from the center of the galaxy?

Not far from the center of the Milky Way galaxy, astronomers have recently witnessed a mysterious flashing of radio waves. Many (in fact, most) objects give off radio waves — this ... Read more »

Infinix Hot 11, Hot 11S launched in India in budget segment: Everything you need to know

Infinix recently launched two new phones in its Hot series in India. The Infinix Hot 11 and Hot 11S arrive in the budget segment and feature MediaTek chipsets, multiple rear ... Read more »

Case of ‘mad cow disease' discovered in Somerset farm

The chief veterinary officer said the infected cow was caught by the government’s strict surveillance programme for BSE (Getty Images/iStockphoto) A case of BSE, commonly known as mad cow disease, ... Read more »

Philips Hue vs WiZ: which smart lights are right for your home?

Adjusting the lighting in your home is a simple way to change the ambiance of a space. For example, if you’re working from home during the day, you may want ... Read more »

iQOO Z5 with Snapdragon 778G, 120Hz display, 5,000 mAh battery to debut in India in sub-30K segment: Report

iQOO is set to unveil a new entrant in the mid-range segment on September 23 in China. The iQOO Z5 will succeed the iQOO Z3, bringing a sizeable battery, an ... Read more »