1. QUANTUM TELEPORTATION
QUANTUM TELEPORTATION
What’s Quantum Teleportation?
Qubits and Quantum Computers

2. TABLE OF CONTENTS
TABLE OF CONTENTS
The theory
Introduction to the Quantum Teleportation
Quantum communication
History, applications, further information
back to the introduction

3. WHAT IS QUANTUM TELEPORTATION?
WHAT IS QUANTUM TELEPORTATION?
Before giving a “complete definition” it is necessary to
emphasize that it is a technique of communication that
takes advantage of some unique aspects of the
Quantum Mechanics
a physical theory that describes
the behaviour of the electromagnetic radiation, the matter
and their interactions, particularly with regard to the
phenomena typical of the length or energy scales of the
atomic and subatomic particles.

4. Development of the Quantum Mechanics
Development of the Quantum Mechanics
The Quantum Mechanics developed in the first half
of the twentieth century, due to the inconsistency
of the classical mechanics and its inability to
represent the experimental reality, with particular
reference to the light and the electron.
The name "Quantum Mechanics", was introduced by
Max Planck in the early twentieth century; it is
based on the fact that quantities such as energy or
angular momentum of some physical systems can
change in a discrete manner namely assuming
only certain values, named:
"QUANTA".
"QUANTA".

5. The basic characteristic that distinguishes the Quantum
Mechanics from the Classical Mechanics is that:
in the Quantum Mechanics the electromagnetic radiation
and the matter are both described as a wave phenomenon
and, at the same time, as particles, in contrast to the
Classical Mechanics, where, for example, the light is
described only as a wave and the electron only as a
particle. This unexpected and non intuitive property called:
“wave-particle duality”
“wave-particle duality”
is the main reason for the failure of all classical
theories developed until the nineteenth century.

6. SOME EXPERIMENTAL SITUATIONS IN WHICH THE
SOME EXPERIMENTAL SITUATIONS IN WHICH THE
"CLASSICAL PHYSICS" FAILS:
"CLASSICAL PHYSICS" FAILS:
Black body radiation
Photoelectric Effect
Atomic spectral lines
Wave properties of the electrons
QUANTUM MECHANICS PROVIDES SOLUTIONS WITH:
QUANTUM MECHANICS PROVIDES SOLUTIONS WITH:
Planck's theory of the radiation of a black body
Einstein's explanation of the photoelectric effect
Bohr's model of the hydrogen atom
Wavelength of Louis de Broglie

7. Max Planck found that the energy of the radiation emitted or absorbed by
a black body is not emitted and absorbed continuously but in discrete
quantities called “quanta”.
The main concept of his theory was based on the fact that:
each elementary oscillator (the electrons within the atom) could exchange
energy with the environment only in the packets form given by:
E = hʋ
where: h = 6,63 × 10-34 J·s = 6,63 x 10-27 erg·s is the Planck's constant
ʋ is the frequency of the oscillator.
Albert Einstein was the first to recognize that this energy quantization of
the emitted or absorbed radiation is a general property of the
electromagnetic radiation, thinking of it as a set of photons with energy:
E = hʋ
Niels Bohr applied the ideas of Einstein, about energy quantization, at
the energy of an atom. He proposed a model of the hydrogen atom
which was a spectacular success in the calculation of the wavelengths of
the radiation emitted by the hydrogen atom.

8. Wave – Particle Duality
Wave – Particle Duality
WAVE AND PARTICLE NATURE OF THE LIGHT
WAVE AND PARTICLE NATURE OF THE LIGHT
Schematic summary
Does the light consist of particles or waves?
The answer depends on the type of observed phenomena.

9. The most common luminous phenomena observed, such as:
reflection, refraction, interference and diffraction
can be explained as wave phenomena.
However, the light that usually we imagine as a wave shows
also particle properties when it interacts with the matter
as demonstrated by the:
photoelectric effect and scattering Compton.
The same “wave-particle” duality is also
valid for the electrons.

10. Wave – Particle Duality
Wave – Particle Duality
WAVE NATURE OF THE MATTER
WAVE NATURE OF THE MATTER
The electrons (and matter in general), which we
usually think as particles, have also
wave properties of interference and
diffraction.

11. Louis de Broglie in 1924 stated that all the particles had wave
properties.
He affirmed that the wavelength associated with the wave of
matter was inversely proportional to the mass “m” of the
particle and to its velocity “v”, so that:
h
λ=
mv
where “h” is Planck's constant.
The product of mass and velocity takes the name of “momentum”
p of the particle, then the equation can be reformulated as “de
Broglie’s relation” in the following way:
h
λ=
p

12. The wave nature of the electrons was revealed showing that
the electron beam can be diffracted.
The experiment was made for the first time in 1925 by two
American scientists, Clinton Davisson and Lester Germer.
They sent a beam of fast electrons against an isolated crystal of
nickel.
The regular arrangement of the atoms in the crystal acts as a
grating, capable of diffracting the waves. Therefore a diffraction
image was observed.
G.P.Thomson, in 1927, operating at Aberdeen, Scotland,
showed that an electron beam produced a diffraction image
passing also through a thin foil of gold, as shown in the figure:

13. Thus even the electron, like the photon, reveals
a double behaviour.
It is not a quite classical particle, but it can have a
detectable wave behaviour.
The wavelength
associated with it is
inversely proportional to its momentum.

14. The “de Broglie’s relation” also applies to
the photons:
λ = c/ν = hc/hν = hc/E = h/(E/c) = h/p
In fact, the momentum of a photon is related to
its energy by the relation: p = E/c

15. CONCLUSION
We can conclude by saying that
"All holders of momentum and energy:
electrons, atoms, light, sound
and so on, have
corpuscular and wave characteristics”.
back to the table of contents

16. COMPARISON BETWEEN CLASSICAL MECHANICS AND
COMPARISON BETWEEN CLASSICAL MECHANICS AND
QUANTUM MECHANICS
QUANTUM MECHANICS
Classical mechanics is a physical theory of
deterministic nature.
It is governed by the principle of causality.
Quantum mechanics is a physical theory of
probabilistic nature.
It is based on the concept of probability and
observation.

17. Basically:
According to the Classical Mechanics, due to the
discoveries of Newton and Galileo Galilei, if you know the
properties of a body (mass, shape, etc.), its initial conditions
of motion (position, velocity, etc.) and the external conditions
(force fields, etc.), it is possible to determine, exactly, its
behavior instant by instant.
Therefore within the framework of the Classical Mechanics
the principle of causality applies; namely, in nature
nothing happens by chance, each event is determined by
an identified cause.
The nature of the Quantum Mechanics is indeterministic;
namely, it is based on the concept of probability and
observation.
For example, if somebody wants accurately to know the
location of an electron in an atom, he will never know the
speed and vice versa.

18. The famous example of Schrödinger's cat clarifies
The famous example of Schrödinger's cat clarifies
the nature of Quantum Mechanics.
the nature of Quantum Mechanics.

19. In this example, a cat is closed in a box, with a machine
connected to a bottle containing poison. The machine
starts when a radioactive element decays, breaking the
bottle containing poison.
From the outside, the cat inside the box can be alive
or dead, because you don’t know if the radioactive
element has decayed or not.
According to the Quantum Mechanics, the cat is in
both states “alive and dead”; it is in a superposition
of states:
state "alive" and state "dead".
Only the observation phase freezes the state of the
cat, determining its fate.

20. In order to speak of Quantum Teleportation it is necessary to take
into account the wave and the corpuscular nature of
electromagnetic radiation and of matter.
That is to say:
“Wave – Particle” duality
for the light and the matter
The wave and the corpuscular nature of
the particles is related by the
“Heisenberg’s Uncertainty Principle”

21. Formulated by the German scientist Werner Heisenberg in 1927, this
principle states that:
“if the uncertainty Δx on the position x of a particle
is very little, the uncertainty Δp on the momentum p
is large and vice versa "
Representation of the Heisenberg’s Uncertainty Principle:
a)
b)
a) The x position of the particle is badly
defined; this allows to specify its
momentum p, represented by the arrow,
with acceptable accuracy.
b) The x position of the particle is well
defined; this prevents to specify precisely
its momentum p.

22. The math expression of the principle is:
Δx·Δp ≥ h/4π
or:
Δx·Δp ≥ ћ/2
According to the Heisenberg’s Uncertainty Principle
we can say that:
“it's impossible to know simultaneously and with
accuracy the momentum and the position of a particle”.

23. The same uncertainty affects the
measurement of energy E and time t:
simultaneous
ΔE·Δt ≥ ћ/2
This means that:
“in a very short time the energy is not defined”.

24. In other words:
“the product of the uncertainties of two
simultaneous measurements can not be
less than a given constant”.
back to the table of contents

25. Quantum communication
Quantum communication
According to Quantum Teleportation it’s possible to
transfer the quantum state of a particle (for example,
the state of polarization, in the case of a photon) to
large distances.
It is not the particle itself to be transferred but the
"receiver" takes exactly the same state of polarization
of the "transmitter".
The Heisenberg’s Uncertainty Principle prohibits the
exact knowledge of the state of the transmitted
photon, but a property called "entanglement" makes
sure that this is not a problem for the teleportation.

26. STAR TREK TELEPORTATION
ALLOWS:
the disappearance of an object from one location and
the simultaneous reappearance of the same object in
another position of the space, without having to travel
boring intermediate kilometers and without any vehicle.

27. In science fiction stories
Teleportation allows to make travels more comfortable than those
made with an ordinary spacecraft, but this involves the violation of
​
the speed limits, imposed by the theory of the relativity.
According to this theory nothing can travel faster than light.
In the science fiction teleportation procedure varies from story to
story and generally takes place in the following way:
the original object to teleport is subjected to a scan to extract the
necessary information to describe it.
A transmitter transfers the information to a receiving station, and this
is used to get an exact replica of the original. In some cases, the
matter, that composes the original, is also transferred to the receiving
station, as some type of energy. In other cases, the replica of the
original uses atoms and molecules already present at the place of
arrival.

28. According to Quantum Mechanics, a similar
impossible even theoretically, in fact:
teleportation is
the Heisenberg’s Uncertainty Principle declares the impossibility of
knowing at the same time, with arbitrary precision, the position and the
velocity of a particle.
A perfect scanning of the object involves the knowledge, without
uncertainty, of the position and the velocity of each atom and each
electron, then teleportation is impossible.
Heisenberg’s principle is also applied to other pairs of quantities and this
expresses the impossibility of measuring, without error, the quantum
state of an object.
All these difficulties, in Star Trek, are overcome by
the prodigious
"Heisenberg’s compensator".

29. BUT
The science-fiction dream of "projecting" objects
from one place to another, is now a reality, at least
for
light particles: photons
although it remains, for now, still a fantasy for
macroscopic objects.

30. QUANTUM TELEPORTATION
QUANTUM TELEPORTATION
Definition:
Definition:
It is a technique of communication within
Quantum Informatics
“this is a group of calculation methods and their study that use
the QUANTA to store and process information”.
The technique of Quantum Teleportation
allows, under certain restrictions, the
transfer of a quantum state,
such as the state of polarization of the photons, the spin state of the
electrons or the excitation state of the atoms,
to a point arbitrarily far.
This involves the effect called
QUANTUM ENTANGLEMENT

31. It can be said that:
by Quantum Teleportation there is not a transfer in the
same way as in Star Trek, but it is possible, through the
phenomenon of entanglement
to transfer (instantly) "features“ (quantum states) of
photons, atoms, ions,
in other
photons, atoms, ions placed at any distance.

32. QUANTUM ENTANGLEMENT
QUANTUM ENTANGLEMENT
The quantum entanglement was suggested for the first time in 1926 by Erwin
Schrödinger, who was also the first to introduce in 1935 the term "entanglement"
Quantum entanglement is a quantum phenomenon, which has no classic equivalent.
According to this phenomenon, each quantum state (e.g.: polarization of the
photons, spin state of the electrons) of two or more physical systems depends on
the state of each of them, even if they are spatially separated.
The quantum entanglement implies the presence of remote correlations between
the observable physical quantities of the involved systems, so that the non-local
character of quantum theory is established.
The phenomenon of entanglement therefore violates the "principle of locality" in
which what happens in one place can NOT immediately affect what happens in
another place.
Albert Einstein, despite the important contributions given to the quantum theory,
never accepted that a particle could instantaneously influence another particle.
Therefore he tried to prove that the violation of locality was only apparent, but, from
time to time, his attempts were clinched by his opponents .

33. In 1982 the physicist Alain Aspect, with a series of
sophisticated experiments demonstrated the existence of
the entanglement, and then the inconsistency of the position
of Einstein.
In October 1998, the phenomenon of the entanglement was
finally confirmed by the success of a teleportation
experiment performed by the Institute of Technology
(Caltech) in Pasadena, California.

34. LEARN MORE ABOUT “ENTANGLEMENT”
LEARN MORE ABOUT “ENTANGLEMENT”
If two particles interact for a certain period of time and then they are
separated, when one of them is stimulated, so that it changes its state,
instantly a similar stress is manifested on the second particle, whatever the
distance between the particles; in other words, the second particle changes
instantaneously its state.
This phenomenon is called "Phenomenon of Entanglement".
A simple experiment about the "Phenomenon of Entanglement”:
two particles “twins” are launched in opposite directions.
If the particle 1, during its journey, meets a magnet that deflects it upward, the
particle 2, instead of continuing its trajectory in a straight line, deflects its
direction at the same time, assuming a motion contrary to that of the particle
1.

35. This experiment demonstrates that:
1. the particles are able to communicate
each other by transmitting and processing
information.
2. the communication is instantaneous.

36. The physicist Niels Bohr said:
"Between two [related] particles that turn away
from one another in space, there is a form of
action - permanent communication. [...]
Although two photons were located on two
different galaxies they would still continue to
remain one entity ..."

37. The experiments of Alain Aspect
The experiments of Alain Aspect
In 1982, Alain Aspect, with the collaboration of the researchers J. Dalibard and G.
Roger of the Optic Institute of the University of Paris, demonstrated the existence of
the entanglement, thus confirming the hypothesis of "non – locality” of the
quantum theory.
The figure shows a simplified scheme of the equipment used by Aspect and his
collaborators during the experiments.
An excited atom of calcium, at the center of the figure, produces a pair of
entangled photons that move along opposite paths “A and B”:

38. Along the path "A“, a birefringent crystal, that acts as a filter, is inserted
from time to time. When the photon interacts with the crystal, it can be
deflected, with a probability of 50%, or it can cross the crystal, continuing
undisturbed on its way. At the end of each path a photon detector is placed
that allows the detection of the photons.
The amazing thing that Aspect observed was that:
when, along the path A, the birefringent crystal was inserted and a deviation
of the photon 1 occurred to the detector C, on the path B, also the photon 2
(photon separate and without "obstacles" in front) deflected "spontaneously"
and “instantly” toward the detector D. Basically, the act of introducing the
birefringent crystal, with the consequent deviation of the photon 1, made
instantly and remotely deflect the photon 2.
This might sound strange, but that's what actually happens when
experiments on pairs of entangled particles are made.
So the idea that entangled particles, located in distant places,
represent separate entities, must be abandoned.

39. In reference to the uniqueness of the matter that
stems from the “non localist” vision of quantum
theory, Brian Josephson (the Nobel Prize for
Physics) says:
"The universe is not a collection of objects, but
an inseparable network of vibrating energy
patterns in which no single component has
independent reality:
including the observer".

40. SCHEMATIC REPRESENTATION OF A QUANTUM TELEPORTATION PROCESS
Transmitted photon
C
Transmitting
station T
A
C
B
A
C
Photon to be
transmitted
Entangled photons
Receiving
station R
B
Source of entangled photons:
Source of entangled photons:
Source EPR
Source EPR
Entanglement is frequently called “EPR effect" from the initials of Albert
Einstein, Boris Podolski and Nathan Rosen. They, in 1935, analyzed the
consequences of particles placed at great distances. The involved particles are
called "EPR pairs”.

41. SHORT DESCRIPTION
SHORT DESCRIPTION
OF THE QUANTUM TELEPORTATION PROCESS
OF THE QUANTUM TELEPORTATION PROCESS
1. Production of a pair of entangled photons A e B by an
appropriate device.
2. Sending of the entangled photons A e B respectively to the
transmitting station T and to the receiving station R.
3. Sending of the photon C, of which you want to teleport the
state of polarization, to the transmitting station T.
4. Interaction, at the start station T, between the photons A
and C and measure on the combined system.

42. 5. Simultaneous change, during the measurement, of the
polarization state of the photon B, at the R station.
6. Communication to the R station, by the traditional media (e.g.:
telephone call), of the result of the measurement on the photon
A and the photon C (4 results are possible).
7. Change of the status of photon B based on the information
communicated.
RESULT
Quantum teleportation of the photon C, this means that a
photon with the same polarization state of the photon C has
been obtained without any measurement on it.

43. More detailed description of the Quantum Teleportation
More detailed description of the Quantum Teleportation
process
process
Amanda and Bert intend to teleport the photon C. Amanda is at the T station and
Bert is at the R station.
At the beginning each receives one photon of an entangled pair:
Amanda receives the photon A and Bert receives the photon B. Instead of carrying
out a measure on the photons, they keep their photon without disturbing the
entangled state.
Amanda receives a third photon C that she wants to teleport to Bert. Amanda in
practice, without knowing the polarization state of the photon C, wants that Bert has a
photon with the same polarization of the photon C.
It is important to notice that Amanda cannot simply measure the polarization state of
the photon C, and then communicate the result to Bert because, for the uncertainty
principle, the measure couldn't accurately reproduce the original state of the photon.
To teleport the photon C, Amanda makes A and C to interact and performs a
measurement on the system, without determining, in absolute terms, the
individual polarizations of the two photons.
The measurement can give 1 of 4 possible results.

44. In technical terms, a joint measurement of this type is called “Bell's state
measurement” and it has a particular effect:
It induces instantly a change in Bert's photon, correlating it to the result
of the measurement performed by Amanda and to the state that the
photon C originally had.
To complete the teleportation, Amanda has to send a message to Bert by the
conventional methods (a phone call or a written note).
After receiving this message, Bert, if necessary, may transform his photon B in
order to make an exact replica of the original photon C.
The transformation that Bert should apply depends on the result of the
measurement of Amanda.
Which of the four possible results Amanda gets, is due to chance. Therefore,
Bert does not know how to modify his photon until he receives from Amanda the
result of the measurement.
After this transformation Bert's photon is in the same state of the photon C.

45. Then, what has been transported is not the photon but its polarization state or,
generally, its quantum state. However, since quantum state is a peculiar
characteristic of a particle, we can say that to teleport a quantum state is like
teleport the particle.
It's important to observe that:
the measurement that Amanda made, connects the photon A to the photon C.
So the photon C loses all the "memory" of its original state. Therefore, the original
state of the C photon, after the measurement, disappears from the place where
Amanda is.
The result of the measurement of Amanda, being totally random, doesn't say
anything about the quantum state.
In this way, the process bypasses the Heisenberg’s principle which doesn't allow
full determination of the state of a particle but allows the teleport of the state,
provided that Amanda doesn't try to know what it is.
The state of the C photon has been transferred without Amanda and Bert had
any knowledge of it.

46. In addition, the teleported quantum information doesn't travel
physically. What is transferred, essentially, is just the message on the
result of the measurement of Amanda that says to Bert how he has to
modify his photon, without any indication on the state of the C photon.
In one of the four cases, the measurement of Amanda is lucky and Bert's
photon becomes immediately a replica of the original.
In this case, it might seem that the information travels instantly from
Amanda to Bert, breaking the limit imposed by Einstein.
It is not so, in fact Bert has no way of knowing that his photon is already a
replica of the original. Only when he learns the result of the measurement
of the Bell's state, performed by Amanda and transmitted to him by the
classical information, he can take advantage of the information about the
teleported quantum state.

47. CONCLUSIONS
CONCLUSIONS
We are still far from the teleportation of a large object. The main problems are:
two entangled objects of the same type are required;
the object that should be teleported and the entangled objects must be
sufficiently isolated from the environment.
If any information is exchanged with the environment, through accidental
interaction, the quantum state of the object degrades in a process called
"decoherence". It is hard to imagine how you can achieve this absolute isolation
for a body of macroscopic dimensions and even more for a human being
because he breathes air and exchanges heat with the outside world. But who can
predict the future developments? Of course we could use existing technology in
order to teleport elementary states, such as those of the photons over distances
of few kilometers, and perhaps even up to the satellites.
The technology that can teleport states of individual atoms has been reached, as
shown by the group led by Serge Haroche of the Ecole Normale Supérieure in
Paris, which has produced entangled atoms.
Entangled molecules and their teleportation can be reasonably expected within the
next decade.
What will happen afterwards, nobody knows.
What will happen afterwards, nobody knows.
back to the table of contents

48. Quantum Teleportation from 1997 to today
Quantum Teleportation from 1997 to today
The first quantum teleportation experiments were carried out between
1993 and 1997, by two international research groups, led respectively by
Francesco De Martini from La Sapienza University in Rome and
Anton Zeilinger from the Institute of Experimental Physics in Vienna.
They were able to teleport the quantum state of a photon.
In 2004:
De Martini carried out a teleportation of photons from one
part to another of the Danube covering a distance of 600
meters.
two groups of scientists, one from the National Institute of
Standards and Technology in the United States and one from
the University of Innsbruck in Austria, were able to teleport
some of the properties of atoms for the first time.
The Americans worked with beryllium atoms while the
Austrians with calcium atoms.

49. In 2006:
some researchers from Niels Bohr Institute in Copenhagen
teleported a collective state from a group of about a trillion
of atoms to another.
The Teleportation applied to the atoms, i.e. to the matter, is a very
delicate process compared to that made on the photons, due to the
process of decoherence. This process, due to interactions with the
environment, destroys the quantum effects, including entanglement.
In 2010:
in China, the researchers of the Hefei National Laboratory for
Physical Sciences reached 16km in the teleportation of
photons without the support of optical fibers.

50. In 2012:
a group of researchers succeeded in realizing the quantum
teleportation of the information relating to a complicated
system of about 100 million of rubidium atoms that had a
magnitude of about one millimeter.
The study was conducted by Jian-Wei Pan of the Hefei National
Laboratory for Physical Sciences at the Microscale, with the
collaboration of the researchers of the University of Science and
Technology in China and of the University of Heidelberg.
For the teleportation, scientists prepared in laboratory an entangled
pair of granules of rubidium. Entangled granules were placed at the
distance of about half a meter and then the two systems were
connected by an optical fiber, 150 meters long and rolled up on itself.
Before performing the process of quantum teleportation, the
scientists mapped the state of excitation of the rubidium atoms in a
photon that traveled along the optical fiber. It was possible to realize
the teleportation by the interaction between the photon "messenger"
with another photon and with the second system of atoms.

51. In 2012:
The team of researchers from the University of Science and
Technology of China in Shanghai, was able to teleport more than
1100 photons in 4 hours covering a distance of 97km of free
space, establishing a new record and overcoming the distance of 16km
obtained from the previous experiment in 2010.
The research team of the Optical Ground Station of the European
Space Agency (ESA) in the Canary Islands settled down a new
world record on the distance about the quantum teleportation,
reproducing the characteristics of a light particle to a distance
of 143km (between Jacobus Kapteyn Telescope La Palma and ESA's
Tenerife Train optical).

52. In 2013:
A group of physicists from the research center Quantop at the
Niels Bohr Institute of the University of Copenhagen has
teleported informations between two clouds of gas atoms of
cesium far from each other half a meter.
The physicists have used two glass containers that were not
connected and the teleportation of the information from one cloud to
another occurred by means of laser light.

53. It is expected that
the next teleportation experiment will
consist of a
Quantum Teleportation between the
Earth and a Satellite in Earth orbit.

54. Applications of the Quantum Teleportation
Realization of quantum computers and networks
Realization of quantum computers and networks
extremely powerful and faster than the actual
extremely powerful and faster than the actual
classical computers and networks.
classical computers and networks.
Exchange of information 100% secure.
Exchange of information 100% secure.
In fact: between the sending station and the receiving
In fact: between the sending station and the receiving
station only one classic signal is exchanged, this doesn't
station only one classic signal is exchanged, this doesn't
allow to a person, who intercepts the classic signal, to
allow to a person, who intercepts the classic signal, to
know the information, in the form of quantum state, that
know the information, in the form of quantum state, that
you are teleporting.
you are teleporting.
Dream of teleportation as in "Star Trek"
Dream of teleportation as in "Star Trek"
back to the introduction

55. QUBITS AND QUANTUM COMPUTERS
QUBITS AND QUANTUM COMPUTERS
BIT (binary digit)
is
the unit of classical information.
QUBIT or quantum bit (quantum binary digit)
is
the unit of quantum information.

56. The "classical bits" operate on binary code and can encode
only one value at a time: 0 or 1.
The "qubits" process the information following the laws of
quantum mechanics and the principle of quantum
superposition, i.e. the idea that an object can exist in
multiple states at the same time; they can take at the same
time the state 0 and 1.

57. In a classical system one bit of information can be represented,
for example, by the voltage applied to the plates of a capacitor:
the charged capacitor denotes the bit 1 and the not charged
capacitor denotes the bit 0.
Quantistically, one bit of information can be encoded using a twolevel system, such as:
the spin states of an electron, the two polarizations of the light.

58. What is a quantum computer?
What is a quantum computer?
The conditions for the realization of quantum computers and quantum
networks, able to offer the best performance in power and speed of
calculation, are provided by the
QUANTUM TELEPORTATION
the phenomenon of teleportation of qubits, achieved by the
quantum phenomenon of entanglement.

59. In a quantum computer the
information would be recorded in
qubits instead of stored in bits as in
a classical computer.

60. How much information can be contained in a
QUBIT?
In practice a Qubit cannot contain more information
than a classical bit, because it assumes the value 0 or
1 when the information is processed.
Therefore a quantum computer does not have
advantages compared to the classical computer, at least
for what concerns the amount of information stored.
The advantage of a quantum computer instead consists
of an exponential increase in computing capability.

61. A quantum processor that can operate on N
Qubits, has the computing power of a
classical processor that operates on 2N bits.
Quantum computers are able to
manage, in a few minutes, lots of
data

62. TECHNOLOGICAL DIFFICULTIES
There are many technological difficulties to be overcome to realize a
quantum computer. One of these is the
decoherence
In other words, the inevitable interaction with the external environment
would destroy, in a short time, the quantum coherence, that is the
information contained in the quantum computer.
At the present, several proposals are under consideration to build a
quantum computer (nuclear magnetic resonance, ion traps, optical systems,
superconducting circuits, etc.), but currently it is not clear which way is the
most likely to succeed.

63. Learn more about:
The roots of entanglement
http://www.scienzaeconoscenza.it/articolo/le-radici-dell-039entanglement.php
The quantum non-separability
http://www.scienzaeconoscenza.it/articolo/la-non-separabilitaquantistica.php
Quantum bits and Quantum Computers
http://phys.org/tags/quantum+bits/
http://phys.org/tags/quantum+computing/
 European Space Agency (ESA)
http://www.esa.int/esasearch?q=quantum+teleportation
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