Quantum1

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6/13/2020
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QUANTUM BEHIND COMPUTING
NAZISH FATIMA UNIVERSITY OF HULL UK CENTRE FOR
PHYSICS EDUCATION (CPE)
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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Suppose I had to travel to a conference on
quantum physics yesterday. After arriving at the
airport I got into a lift and exited on two
floors at the same time. Then I simultaneously
got on a plane to Toronto and to Singapore. My
friends greeted me in Singapore. I never did
arrive in Toronto.
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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This may seem like a convoluted way to earn
double air miles,
But if I were a photon or an electron, being in
two places at once, or in a quantum
superposition, it would not be so
unusual. Quantum physics seems strange to us.
Because we do not clearly see its influence on
the world around us
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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Over the last century, physicists have discovered
when you go down to a really small scale, weird
things start to happen. Theyve developed a
whole new field of science to try and explain
them. Its called Quantum mechanics
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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• Classical physics says Waves and Particles are
  two different things
• A particle can exist OR cannot exist
• Or it can be at position A OR at position B
• Interference , Diffraction, Superposition etc.
  are the properties associated with waves
• Quantum physics says there is a wave associated
  with every particle
• So particle can exist AND not exist at the same
  time
• A particle can be at position A AND position B at
  the same time
• The wave associated with particle superimpose and
  interfere and make it possible

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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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ull ,UK, Emai ma-2018_at_hull
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LET US GO BACK TO
OUR LIFE
EXPERIENCES

• Our mobile phone, if it's a modern smartphone,
  knows where you are on the planet, all the time,
  often to within metres
• How does your phone do that?
• The answer is, of course via the Global
  Positioning System, or GPS

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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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• At any time there are between 24 and 32 working
  GPS satellites in orbit, roughly at an altitude
  of 20,000 kilometres, and if your phone can
  receive signals from at least four of them
• The satellites know where they are relative to
  Earth, and in turn they will tell your mobile
  phone
• The time delay in receiving the message from the
  satellite on your phone determines how far away
  the satellite is from your phone
• Distance is time delay times the speed
• of light
• Knowing the distance to four satellites then
  allows your phone to triangulate and establish
  where it is. Simple!
• 6/13/2020 Dept.of Physics, University of Hull
  ,UK, Email n.fatima-2018_at_hull.ac.uk

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LET'S THINK A BIT MORE ABOUT THE PRECISION OF GPS

• Light travels about 30 cm in one nanosecond, so
  in order to get your location down to within a
  metre, the error in the time delay can only be a
  few nanoseconds
• To get that precision, normal clocks are not
  sufficient and we need to use much more precise
  atomic clocks
• These clocks monitor the atomic transition
  between the ground state and first excited state
  of a caesium-133 atom, which produces radiation
  with exactly 9,192,631,770 cycles per second
• To calculate how the caesium atom jumps between
  these two states, and how we can read this out in
  a practical clock, we need quantum mechanics

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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
6/13/2020
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SO YOU KNOW WHERE YOU ARE ON THE PLANET EVERY
TIME YOU CHECK YOUR PHONE'S MAP BECAUSE OF
QUANTUM MECHANICS!
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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ANOTHER WAY IN WHICH QUANTUM MECHANICS IMPACTS
YOUR LIFE IS VIA TRANSISTORS

• Tiny devices, a few tens of nanometres
• Typically made from silicon, gallium arsenide,
  or some other semiconducting material
• Transistors are used as very fast current
  switches in microchips, and they can be made to
  perform logic operations
• A typical mobile phone chip has several
• billion transistors

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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
6/13/2020
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WHILE WE ARE ALL HAPPILY TASTING THE FRUITS OF
QUANTUM MECHANICS IN OUR DAILY LIVES, QUANTUM
PHYSICISTS ARE WORKING OUT HOW TO BUILD THE NEXT
BIG THING
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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LIKE COMPUTERS PERHAPS
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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
6/13/2020
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Quantum Computing Focuses On The Principles Of
Quantum Theory, Which Deals With Modern Physics
That Explain The Behaviour Of Matter And Energy
Of An Atomic And Subatomic Level.
Quantum Computing Makes Use
Of Quantum Phenomena, Such As Quantum Bits,
Superposition, And Entanglement To Perform Data
Operations
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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WHAT WE HAVE IN
CONVENTIONAL COMPUTING

• The actual logic carried out on the computers,
  the zeros and ones if you like, is following the
  standard rules formulated by George Boole in the
  nineteenth century
• The "bit", is an abstract idea that represents a
• physical system that can be in two distinct
  states
• The system is either in one state or another
• For example, a light bulb can be on or off, a
  wire in a computer can carry a current or not, a
  capacitor can carry a charge or no charge

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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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SO THE LOGIC FOR CONVENTIONAL COMPUTING IS
020
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NOW LET'S SEE HOW QUANTUM MECHANICS ALLOWS US TO
MOVE BEYOND BOOLEAN LOGIC FOR COMPUTERS
6/13/2020
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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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LET'S RETURN TO THE CAESIUM ATOM IN THE ATOMIC
CLOCK.

• It has two states, the ground state
• and the first excited state
• We can also call these two states zero and one,
  giving us a truly tiny bit
• But it gives us more
• The caesium atom can be in one of these two
  states, and also in any quantum superposition
  of these two states
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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IN A QUANTUM COMPUTER,
THE BASIC UNIT OF MEMORY IS A QUANTUM BIT OR
QUBIT. QUBITS ARE MADE USING PHYSICAL SYSTEMS,
SUCH AS THE SPIN OF AN ELECTRON OR THE
ORIENTATION OF A PHOTON. THESE SYSTEMS CAN BE IN
MANY DIFFERENT ARRANGEMENTS ALL AT ONCE, A
PROPERTY KNOWN AS QUANTUM SUPERPOSITION.
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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1930s Copenhagen interpretation, developed in
the Danish city by luminaries of quantum
theory, Niels Bohr and Werner Heisenberg says
that there really is no definitive reality
before the measurement, and the object is in an
undefined state known as a superposition.
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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NOW WHAT EXACTLY IS QUANTUM SUPERPOSITION ????
The principle of quantum superposition states
simply that a quantum particle can exists in 2
distinct locations at the same time. According
to this theory, a quantum particle can exist
simultaneously in multiple states, unless the
operation of measurement is made
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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LETS MAKE IT A BIT MORE SIMPLE
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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He imagined a box containing a radioactive atom,
a vial of poison and a cat. Governed by quantum
rules, the radioactive atom can either decay or
not at any given moment. Theres no telling when
the moment will come, but when it does decay, it
breaks the vial, releases the poison and kills
the cat.
If the Copenhagen interpretation is correct, then
before any measurement has occurred, the atom,
and so also the cat, are in a superposition of
being decayed/dead and not decayed/alive
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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
6/13/2020
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• Superposition makes qubits interesting, but their
  real superpower is entanglement. Entangled
  qubits can interact instantly. To make
  functional qubits, quantum computers must be
  cooled to near absolute zero.
• Even when supercooled, qubits dont maintain their

entangled state (coherence) for very long
6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
6/13/2020
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QUBITS CAN ALSO BE INEXTRICABLY LINKED TOGETHER
USING QUANTUM
ENTANGLEMENT. THE RESULT IS THAT A SERIES OF
QUBITS CAN REPRESENT DIFFERENT THINGS
SIMULTANEOUSLY
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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Quantum mechanics is the foundation of physics,
which underlies chemistry, which is the
foundation of biology. So for scientists to
accurately simulate any of those things, they
need a better way of making calculations that
can handle uncertainty.
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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QUANTUM COMPUTERS

• Quantum computers will find a use anywhere where
  theres a large, uncertain complicated system
  that needs to be simulated. That could be
  anything from predicting the financial markets,
  to improving weather forecasts, to modelling the
  behaviour of individual electrons using quantum
  computing to understand quantum physics
• That could mean more efficient products from
  new materials for batteries in electric cars,
  through to better and cheaper drugs, or vastly
  improved solar panels. Scientists hope that
  quantum simulations could even help find a cure
  for Alzheimers.
• Cryptography will be another key application.
  Right now, a lot of encryption systems rely on
  the difficulty of breaking down large numbers
  into prime numbers. This is called factoring,
  and for classical computers, its slow, expensive
  and impractical. But quantum computers can do it
  easily. And that could put our data at risk

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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk
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6/13/2020
Dept.of Physics, University of Hull ,UK, Email
n.fatima-2018_at_hull.ac.uk