Quantum Physics
Quantum Physics
Physics - Overview
Classical Physics
Daily life
Macrocosmos (universe)
Quantum Physics
Microcosmos (atom)
Quantum Physics
What is Quantum Physics?
In physics, a quantum is the minimum of any physical entity involved in an interaction.
Fundamental physical property may be ’quantized’.
Quantum Physics is a branch of physics
providing a mathematical description of microcosmos (atoms, elementary particles, …)
Microcosmos (atom)
Quantum Physics
Microcosmos
1000*distance
earth/sun
Atom
Diameter = 1 km
99.999999999999 %
of the atom is empty space
Quantum Physics
Microcosmos in our daily life
Quantum Physics
Microcosmos in our daily life - Future
Quantum Computer
Quantum Computer
A quantum computer is a device for computation that makes direct use of quantum physical phenomena,
such as superposition and entanglement to perform operations on data.
Quantum computers are different from traditional computers based on transistors.
The basic principle behind quantum computation is that quantum properties can be used to represent data
and perform operations on these data.
Experiments have been carried out where quantum computational operations were executed on
number of qubits (quantum bits).
Quantum Physics
Microcosmos in our daily life - Future
Quantum Cryptograhpy
Cryptography
Cryptography is the practice and study of hiding information.
Modern crypthography intersects the disciplines of mathematics, computer science and electrical engineering.
Quantum cryptography describes the use of quantum physics effects.
Well-known examples of quantum cryptography are the use of quantum communication
to securely exchange a key (quantum key distribution).
The advantage of quantum cryptography lies in the fact that it allows the completions of
various cryptographic tasks that er proven to be impossible using only classical communications.
In particular, quantum physics guarantees that measuring quantum data disturbs the data,
this can be used to detect an adversary’s interference with a message.
Quantum Physics
Microcosmos in our daily life - Future
Quantum secured bank transfer
Quantum secured bank transfer
Quantum Physics
Physics - History
2000
.
.
.
.
.
.
.
Quantum physics
Theory of relativity
1900
Microcosmos
Electromagnetism
Thermophysics
Planetary motion
Mechanics
.
Quantum Physics
Planck’s law of blackbody radiation
2hν 3
I(ν, T )  2
c
1
e
hν
kT
1
Quantum of Energy
Quantum Physics
Photoelectric Effect
Light cannot be explained purely as a wave phenomenon
Quantum Physics
Compton scattering
Light cannot be explained purely as a wave phenomenon
Quantum Physics
Double Slit Experiment
Quantum Physics
Mach-Zhender interferometer
2
2
R2
2
2
In1
6
Out2
4
5 
1
Out1
S2
2
3
S1
1
1
4-6
1
R1
2-4
S1
0.25
S2
0.5
4-5
5
0.25
0.5
3-5 5
0.25
3-6 6
0.25
1-3
1
6
S2
Classical physics
Out1 :
Out2 :
3-5 + 4-5 = 0.25 + 0.25 = 0.5
3-6 + 4-6 = 0.25 + 0.25 = 0.5
Quantum physics
Out1 :
Out2 :
1
0
Quantum Physics
Entanglement
Quantum entanglement is a physical resource (in a way like energy)
associated with the nonclassical correlations that are possible between separated quantum systems.
A pair of quantum systems in an entangled state can be used as a quantum information channel to
perform computational and cryptographic tasks that are impossible for classical systems.
Quantum Physics
x-ray
Quantum Physics
Strange Questions
An apple is laying on a table.
You measure the position of the apple on the table.
Question:
Where was the apple just before your measurement?
Question:
Is it possible for a person to be at two different places
at the same time?
Question:
Is it possible for two persons to interact
without any kind of communication?
Quantum Physics
Understanding
The mankind has all time
been thinking of beeing
in the centre of the world,
the earth, the planetary system,
Milky Way, …
How can we imagine
we are seeing almost the whole world,
we are only seeing a little part of
the electromagnetic spectrum.
In microcosmos
we have to learn again almost everything,
we almost have no models / pictures /
conceptions, common sense, …
Quantum Physics
Relativity - Addition of velocities
Classic:
vx  v  vx '
 100
vx '
km
km
km
5
 105
h
h
h
v
Relativity:
v  vx '
vv '
1 2x
c
km
km
100  5
km
h
h

 105
km km
h
100  5
h
h
1
2
km 

8
 3 10  3.6

h 

vx 
vx
km
h
km
v  100
h
vx '  5
The velocity of the person
relative to the earth
The velocity of the person
relative to the train
The velocity of the train
relative to the earth
Quantum Physics
GPS - Relativity
Because of the high speed,
the time moves more slowly
in the satellites.
Because we are closer
to the center of the earth,
the time moves more slowly
on the earth.
The last effect is greater,
therefore the time goes more slowly
on the earth than in the satellite.
We have to use Einstein’s theory of relativity
to adjust the time.
If not, the GPS would give a result
several kilometers out of position.
Quantum Physics
Strange situations in microcosmos
A measurement of a system
cause a change of the state of the system
Measuring the door
makes the door
smaller
A system can be in a superposition
of different states at the same time
Going through two
doors
at the same time
Two different systems far away from each other
can affect each other momentarily
though no communication
Changing spin
of one of the two particles
change spin of the other
though no communication
Quantum Physics
Classical Physics  Quantum Physics
Classical
Physics
Quantum
Physics
Strange situations in daily life
that happens in micro cosmos [1/2]
You have parked your car.
If you know your car is parked (zero velocity),
it’s impossible to find it, it can be anywhere.
Quantum Physics
Classical Physics  Quantum Physics
Classical
Physics
Quantum
Physics
Strange situations in daily life
that happens in micro cosmos [2/2]
. . . . . . .
The laser changes the speed of the car.
It’s the laser control that gives the car it’s speed.
The measuring changes the high of the car so it cannot pass the tunnel.
Always different colors of clothes
though they don’t communicate.
The cat is both dead and alive
until something controls it.
Quantum Physics
Quotation
Niels Bohr:
If you are not confused by quantum physics
then you haven’t really understood it.
Richard Feynman:
I think I can safely say
that nobody understands quantum physics.
J.B:Haldane:
The universe is not only more strange than we suppose,
but more strange that we are able to suppose.
Daniel Greenberger:
Einstein said that if quantum physics
were correct, then the world would be crazy.
Einstein was right, the world is crazy.
William D. Phillips:
Entanglements, along with the superposition states,
is the strangest thing about quantum physics.
Davied Bohm:
The most fundamental theory now available
is probabilistic in form, not deterministic.
Kvantefysikk
Innføring
Fysikk
Matematikk
F  ma
0 1 2 3 …
 p2



V


i
h
 E


2
m

t


h
p 
i
 h2 2





V


i
h
 E


2
m

t


0
1
Quantum Physics
Statistics - Discrete Variables - Continuous Variables
Discrete Variables
Probability
Probability density
Pi 
Continuous Variables
Ni
N
(x)dx


Total probability
1   Pi
1   ( x )dx
i 0



Expectation value
i   iPi
x   x( x )dx
i 0



f (i)   f (i)  Pi
f (x)   f (x)(x)dx
i 0

Variance
 2  (i) 2  i 2  i
Standard deviation
  (i)

2
 i
1
2
2
 2  (x ) 2  x 2  x
2
 i
2

1
2

  (x)
2
  x
1
2
2
2
 x
2

1
2
Kvantefysikk
Kvantefysikk:
Størrelser som inngår i beskrivelse av materien og dens vekselvirkning
kan bare anta bestemte, kvantiserte, verdier
og ikke forandre seg kontinuerlig fra en verdi til en annen.
1900 Plancks strålingslov
1905 Einstein fotoelektrisk effekt
En energimengde E = hf svarende til hver frekvens f.
Lys som fotoner eller energikvanter med energi E = hf
h Plancks konstant 6.626 10-34 Js.
Usikkerhetsrelasjon (uskarphetsrelasjon):
x  p 
h
2