# Quantum Computing - PowerPoint PPT Presentation

View by Category
Title:

## Quantum Computing

Description:

### This Presentation describes the concept of Quantum Computing. – PowerPoint PPT presentation

Number of Views:53
Slides: 26
Provided by: vishal_18
Tags:
Transcript and Presenter's Notes

Title: Quantum Computing

1
Quantum Computing
• Prepared by Vishal Garg
• CSE 5th Semester

2
What is Quantum Computing?
• Quantum computing is the computer technology
based on the principles of quantum theory, which
explains the nature and behaviour of energy and
matter on the quantum (atomic and subatomic)
level.
• Quantum computing is essentially harnessing and
exploiting the amazing laws of quantum mechanics
to process information.

3
What Is Quantum?
• A classical binary bit is always in one of two
states0 or 1while a quantum bit or qubit exists
in both of its possible states at once, a
condition known as a superposition.
• An operation on a qubit thus exploits its quantum
weirdness by allowing many computations to be
performed in parallel.
• A two-qubit system would perform the operation
on 4 values, a three-qubit system on 8 and so
forth.

4
What Is Quantum?
5
What Is Quantum?
• Rather than performing each calculation in turn
on the current single state of its bits, as a
classical computer does, a quantum computer's
sequence of qubits can be in every possible
combination of 1s and 0s at once.
• This allows the computer to test every possible
solution simultaneously and to perform certain
complex calculations exponentially faster than a
classical computer.
• One curious feature of a qubit is that measuring
it causes it to "collapse" into a single
classical known state0 or 1 againand lose its
quantum properties.

6
What Is Quantum?
• Many quantum algorithms are non-deterministic
they find many different solutions in parallel,
only one of which can be measured, so they
provide the correct solution with only a certain
known probability.
• Running the calculation several times will
increase the chances of finding the correct
answer but also may reduce quantum computing's

7
History of Quantum Computing
• Quantum computing tends to trace its roots back
to a 1959 speech by Richard P. Feynman in which
he spoke about the idea of exploiting quantum
effects to create more powerful computers.
• This speech is also generally considered the
starting point of nanotechnology.
• In 1984, David Deutsch was at a computation
theory conference and began to wonder about the
possibility of designing a computer that was
based exclusively on quantum rules, then
published his breakthrough paper a few months
later.
• With this, the race began to exploit his idea.

8
History of Quantum Computing
• In 1994, ATT's Peter Shor devised an algorithm
that could use only 6 qubits to perform some
basic factorizations ... more cubits the more
complex the numbers requiring factorization
became, of course.
• The first, a 2-qubit quantum computer in 1998,
could perform trivial calculations before losing
decoherence after a few nanoseconds.
• In 2000, teams successfully built both a 4-qubit
and a 7-qubit quantum computer.
• Research on the subject is still very active,
although some physicists and engineers express
concerns over the difficulties involved in
upscaling these experiments to full-scale
computing systems.

9
How a Quantum Computer Would Work?
• A quantum computer, would store information as
either a 1, 0, or a quantum superposition of the
two states. Such a "quantum bit," called a qubit,
allows for far greater flexibility than the
binary system.
• Specifically, a quantum computer would be able to
perform calculations on a far greater order of
magnitude than traditional computers ... a
concept which has serious concerns and
applications in the realm of cryptography
encryption.
• Some fear that a successful practical quantum
computer would devastate the world's financial
system by ripping through their computer security
encryptions, which are based on factoring large
numbers that literally cannot be cracked by
traditional computers within the life span of the
universe.
• A quantum computer, on the other hand, could
factor the numbers in a reasonable period of time.

10
How a Quantum Computer Would Work?
• If the qubit is in a superposition of the 1 state
and the 0 state, and it performed an calculation
with another qubit in the same superposition,
then one calculation actually obtains 4 results
a 1/1 result, a 1/0 result, a 0/1 result, and a
0/0 result.
• This is a result of the mathematics applied to a
quantum system when in a state of decoherence,
which lasts while it is in a superposition of
states until it collapses down into one state.
• The ability of a quantum computer to perform
multiple computations simultaneously (or in
parallel, in computer terms) is called quantum
parallelism).

11
How a Quantum Computer Would Work?
• if there are n qubits in the supercomputer, then
it will have 2n different states.
as compared to regular digital bits thereby
increasing the speed of the system exponentially.
• The qubits are dynamic and are only the
probabilistic superposition of all of their
states.
• So, the accurate measurement is difficult and
requires complex algorithms such as Shors
algorithm

12
Superposition and Entanglement?
• Superposition is essentially the ability of a
quantum system to be in multiple states at the
same time that is, something can be here and
there, or up and down at the same time.
• Entanglement is an extremely strong correlation
that exists between quantum particles so
strong, in fact, that two or more quantum
particles can be inextricably linked in perfect
unison, even if separated by great distances.
• The particles are so intrinsically connected,
they can be said to dance in instantaneous,
perfect unison, even when placed at opposite ends
of the universe.
• This seemingly impossible connection inspired
Einstein to describe entanglement as spooky
action at a distance.

13
What can a quantum computer do that a classical
computer cant?
• Factoring large numbers, for starters.
• Multiplying two large numbers is easy for any
computer.
• But calculating the factors of a very large (say,
500-digit) number, on the other hand, is
considered impossible for any classical computer.
• In 1994, a mathematician from the Massachusetts
Institute of Technology (MIT) Peter Shor, who was
working at ATT at the time, unveiled that if a
fully working quantum computer was available, it
could factor large numbers easily.

14
I dont want to factor very large numbers
• In fact, the difficulty of factoring big numbers
is the basis for much of our present day
cryptography.
• RSA encryption, the method used to encrypt your
credit card number when youre shopping online,
relies completely on the factoring problem.
• Since factoring is very hard, no eavesdropper
will be able to access your credit card number
and your bank account is safe.
• Unless, that is, somebody has built a quantum
computer and is running Peter Shor's algorithm!

15
So a quantum computer will be able to hack into
my private data?
• Dont worry classical cryptography is not
completely jeopardized.
• This is where quantum mechanics comes in very
handy once again
• Quantum Key Distribution (QKD) allows for
the distribution of completely random keys at
a distance.

16
How can quantum mechanics create these
ultra-secret keys?
• Quantum key distribution relies on another
interesting property of quantum mechanics any
attempt to observe or measure a quantum system
will disturb it.
• Photons have a unique measurable property called
polarization.

17
What is required to build a quantum computer?
• We need qubits that behave the way we want them
to.
• These qubits could be made of photons, atoms,
electrons, molecules or perhaps something else.
• Scientists at IQC are researching a large array
of them as potential bases for quantum computers.
• But qubits are notoriously tricky to manipulate,
since any disturbance causes them to fall out of
their quantum state (or decohere).

18
What is required to build a quantum computer?
• The field of quantum error correction examines
how to stave off decoherence and combat other
errors.
• Every day, researchers at IQC and around the
world are discovering new ways to make qubits
cooperate.

19
Challenges To Quantum Computing
• Decoherence
• One of the biggest challenges is to remove
quantum decoherence.
• Decoherence in a laymans language could be
understood as the loss of information to the
environment. The decoherence of the qubits occurs
when the system interacts with the surrounding in
a thermodynamically irreversible manner.
• So, the system needs to be carefully isolated.
Freezing the qubits is one of the ways to prevent
decoherence.

20
Challenges To Quantum Computing
• Interference
• During the computation phase of a quantum
calculation, the slightest disturbance in a
quantum system (say a stray photon or wave of EM
radiation) causes the quantum computation to
collapse, a process known as de-coherence.
• A quantum computer must be totally isolated from
all external interference during the computation
phase.
• Some success has been achieved with the use of
qubits in intense magnetic fields, with the use
of ions.

21
Challenges To Quantum Computing
• Error correction
• Because truly isolating a quantum system has
proven so difficult, error correction systems for
quantum computations have been developed.
• Qubits are not digital bits of data, thus they
cannot use conventional (and very effective)
error correction, such as the triple redundant
method.
• Given the nature of quantum computing, error
correction is ultra critical - even a single
error in a calculation can cause the validity of
the entire computation to collapse.

22
Challenges To Quantum Computing
• Output observance
• Closely related to the above two, retrieving
output data after a quantum calculation is
complete risks corrupting the data.
• In an example of a quantum computer with 500
qubits, we have a 1 in 2500 chance of observing
the right output if we quantify the output.
• Thus, what is needed is a method to ensure that,
as soon as all calculations are made and the act
of observation takes place, the observed value
will correspond to the correct answer.
• How can this be done? It has been achieved by
Grover with his database search algorithm, that
relies on the special "wave" shape of the
probability curve inherent in quantum computers,
that ensures, once all calculations are done, the
act of measurement will see the quantum state

23
If Its So Complex, Why Is Everyone After Quantum
Computing?
• A fully functional quantum computer would require
around a million atoms. And right now, we are at
a mere thousand.
• But, what would happen if we reach that limit or
even its half?
• Genome sequencing or Tracking weather patterns
• Second, the modern day encryption systems are
entirely based on the limitations of the regular
computers.
• Quantum computing wont be of changing your lives
in day to day operations, but a quantum
communication network would definitely provide a
better and secure network.

24
Thank You So Much for Being a Active Listener
25
QUERIES ??? (if any......)