Quantum entanglement: “Spooky action at distance” in the lab,...

Quantum entanglement: “Spooky action at distance”

in the lab, and in black holes

Tilde Cafe, Branford CTNovember 9, 2019

Subir Sachdev

HARVARD

Talk online: sachdev.physics.harvard.edu

http://nyti.ms/1OIO2WJ

SCIENCE

Sorry, Einstein. Quantum Study Suggests‘Spooky Action’ Is Real.By JOHN MARKOFF OCT. 21, 2015

In a landmark study, scientists at Delft University of Technology in theNetherlands reported that they had conducted an experiment that they say provedone of the most fundamental claims of quantum theory — that objects separated bygreat distance can instantaneously affect each other’s behavior.

The finding is another blow to one of the bedrock principles of standardphysics known as “locality,” which states that an object is directly influenced onlyby its immediate surroundings. The Delft study, published Wednesday in thejournal Nature, lends further credence to an idea that Einstein famously rejected.He said quantum theory necessitated “spooky action at a distance,” and he refusedto accept the notion that the universe could behave in such a strange andapparently random fashion.

In particular, Einstein derided the idea that separate particles could be“entangled” so completely that measuring one particle would instantaneouslyinfluence the other, regardless of the distance separating them.

Einstein was deeply unhappy with the uncertainty introduced by quantumtheory and described its implications as akin to God’s playing dice.

But since the 1970s, a series of precise experiments by physicists are1 of 2

Part of the laboratory setup for an experiment

at Delft University of Technology, in which

two diamonds were set 1.3 kilometers apart, entangled and then shared information.

Quantum phase transitions

Quantum entanglement

The double slit experiment

Interference of water waves

Principles of Quantum Mechanics: 1. Quantum Superposition

TWO$SLITS$

Bullets

Send electrons through the slits

Interference of electrons

Is the electron a wave ?

TWO$SLITS$

Unlike water waves, electrons arrive one-by-one

(so is it like a particle ?)

But if it is like a

particle, which slit does each

electron pass through ?

No interference when you watch the electrons

But if it is like a

Each electron passes

through both slits !

But if it is like a

Let |L� represent the statewith the electron in the left slit

And |R� represents the statewith the electron in the right slit

|L� |R�

And |R� represents the statewith the electron in the right slit

|L� |R�

Actual state of each electron is|Li + |Ri

Quantum Entanglement: quantum superposition with more than one particle

Principles of Quantum Mechanics: 1I. Quantum Entanglement

Hydrogen atom:

=1⌃2

(|⇥⇤⌅ � |⇤⇥⌅)

Hydrogen molecule:

Einstein-Podolsky-Rosen “paradox” (1935): Measurement of one particle instantaneously

determines the state of the other particle arbitrarily far away

Black holes

Horizon radius R =2GM

Objects so dense that light is gravitationally bound to them.

Black Holes

In Einstein’s theory, the region inside the black hole horizon is disconnected from

the rest of the universe.

On September 14, 2015, LIGO detected the merger of two black holes, each weighing about 30 solar masses, with radii of about 100 km, 1.3 billion light years away

0.1 seconds later !

Around 1974, Bekenstein and Hawking showed that the application of the

quantum theory across a black hole horizon led to many astonishing

conclusions

Black Holes + Quantum theory

Quantum Entanglement across a black hole horizon

Black hole horizon

There is long-range quantum entanglement between the inside

and outside of a black hole

Black hole horizon

Hawking used this to show that black hole horizons have an entropy and a temperature

Black hole horizon

Hawking used this to show that black hole horizons have an entropy and a temperature

(because to an outside observer, the state of the electron inside the black hole is an unknown)

Black holes

Superconductors

Black holes

YBa2Cu3O6+x

High temperature superconductors

Julian Hetel and Nandini Trivedi, Ohio State University

Nd-Fe-B magnets, YBaCuO superconductor

Efficient Rotating Machines

Power Efficiency/Capacity/Stability Power Bottlenecks Accommodate Renewable Power

Information Technology Next Generation HEP

HE Accelerators Science / Medicine

Ultra-High Magnetic Fields TransportMedical

Slide by J. C. Seamus Davis

Square lattice of Cu sites

Remove some electrons

= | ⇥⇤⌅ � | ⇤⇥⌅

Electrons entangle in (“Cooper”) pairs into chemical bonds

Electrons entangle “en masse” by exchanging partners, and there is long-range quantum entanglement

= | ⇥⇤⌅ � | ⇤⇥⌅

Superconductors

Black holes

A “toy model” which describes both a superconductor and a black hole!

Superconductors

The Sachdev-Ye-Kitaev (SYK) model

Pick a set of random positions

Place electrons randomly on some sites

The SYK model

Place electrons randomly on some sites

Entangle electrons pairwise randomly

The SYK model

This describes both a superconductor and a black hole!

Maxwell’s electromagnetism and Einstein’s general relativity

allow black hole solutions with a net charge

Zooming into the near-horizon region of a

charged black hole at low temperature, yields

a quantum theory in one space ( ) and one

time dimension⇣

The quantum versions of Maxwell’s and

Einstein’s equations in this two-dimensional

spacetime are also the equations describing

electron entanglement in the SYK model

This has led to a deeper understanding

of entanglement in superconductors and

of Hawking’s black hole information “paradox”

Black holes

A “toy model” which describes both a superconductor and a black hole!

Superconductors

Quantum entanglement: “Spooky action at distance” in the lab,...

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