Download How to program a quantum computer

Different methods of quantum
computing optimization
- Jeremy Zhao
Introduction
In order to understand quantum computing you need to understand
how a conventional computer works.
In a conventional computer there are
transistor which are small switches that
can be turn on and off. The computer
can read the information as 1,0 to
determine the information. ( The picture
on the left is a picture of a quantum gate
which is very similar to a transistor)
Moore’s Law
Since 1965 there is a special pattern of
computing power increase it’s called “Moore's
law” , It said that the number of number of
transistors in a dense integrated circuit doubles
approximately every 18 month and it was
named after the co-founder of intel who
observed this pattern in 1965.
Because of Moore’s law the computing
power was growing rapidly from 1970s to
early 2000s. Essentially the computing
power will nearly double for cpus for every
18 month.
The issue of Moore’s Law is when the gap
between the Source and Drain are too small
there is a quantum mechanic which will kick
in it’s called “tunnelling”. It basically will make
electrons jump through the barely no matter
what kind of material it’s made out of. Due to
this mechanic the traditional computer will
reach a bottle neck of computing power very
soon.
Right now computing chip set manufacture
like intel and amd are focus on features and
optimization.
In order to put more transistor on to a
reasonably sized chip they have to make
transistor smaller. The easiest way to make
that happen is to shorten the gap between
the Source and the Drain.
What is a quantum computing?
Quantum Computing is a method of
computing which use Quantum
Mechanics. It use Quantum Bits for unit
of information. Due to the nature of
Qubits it can solve and calculate certain
problems much faster, like weather
predication and computer deep
learning.
How does a quantum computer works?
A few important things to learn about quantum computers are:
1. Qubits
2. Qubit spins
3. Quantum Superposition
4. Quantum Entanglement
Qubit
Quantum Bits(Qubits) are the most
essential part of the quantum
computer, they are what made
quantum computer quantum
computer. They are units of
information that Quantum Computer
use, Just like bits for classic
computers. But unlike a transistor
used in classic computer, qubits are
normally made up with a single
nucleus or election.
What makes qubit so special?
In quantum computing there is allergy which
is “spin” it refers to the position of qubit as
we measure it, normally we refer to the low
energy state of the qubit as spin down and
the high energy state of the qubit as spin
up.(EX: a electron in a magnetic field when
it’s alien with the field it’s spin down because
it has low energy) It can be the equivalent to
0,1 in classical computer( spin up and down).
In order to understand the special
property of a qubit we need to understand
a few concept, let’s start with spins.
What makes qubit so special?
Super position, it’s a very weird concept in
quantum mechanic I will try my best to
explain.
In essence a quantum object can be in
multiply state at the same time, but when
the object get measured it can only be in
one of two basic state- spin up or down.
Quantum Entanglement
In essence why quantum computer has the
superior performance against a normal
computer is when a qubit is in a
superposition they can be a probability of
two states(spin up, spin down in relative to
the measurement) and due to that in a 2 bit
quantum entanglement like the diagram
showed on the left, need 4 confident
information to solve because qubits can be in
the probability of any of these four combos.
Unlike a normal 2 bit system(11,00,10,01)
with a classical 2 bits system we only need to
know the value of the first bit and the value
of the second bit to know any of the four
combos, so it only contains 2 bits of
information. But in the 2 bit quantum
entangled combo you need 4 confident to
determine the information so this system
contains 4 bits of information.
• Quantum Entanglement
So in a 3 bit system it will contain 8 bits of information, and
with N qubits it will contain 2N bits of information, with the
power of exponential if we have 300 bits that’s more than all
particles in the universe in equivalent classical bit information.
But there is a catch, qubits can only be measured in 2 basic
states so the logic of the computer have to be designed in
such a way that the end product is not in superposition
because it can’t be measured. One cool thing about
entanglement is no matter the distance between the qubits
they are always entangled, so one qubit can be in outer space
when you measure the other qubit which it’s entangled to it
will still be in the entangled state with the other one no
matter it’s opposite of the same as the other, and the
reasoning behind this is still being researched.
Different types of quantum
computers
There are few different approaches to quantum computing and utilize the potential of
the qubits:
Quantum Annealing
• Universal Quantum Computing:
Measurement Base Quantum Computing
Adiabatic Quantum Computing
Topological Quantum Computing
Quantum Annealing
Quantum Annealing is the only
types a quantum computing
which is not in experimental
phase and it’s one of the
relatively easy approach to
quantum computing, and it’s
the only type of quantum
computing which is not under
the category of universal
quantum computing or gate
model quantum computing.
Quantum Annealing, difference between gate model and quantum annealing
Quantum Annealing is a process which is
unique and it’s a very different approach
than gate model quantum computing. In
quantum annealing scientist trying to use
the nature of physics which everything
wants to get to a lower energy state to
harness the power of quantum computing,
aka they setup the problem and let
quantum mechanics do it’s own thing of
finding a lower energy state. On the other
hand gate model quantum computing is
more ambitious their target is to
manipulate the process of quantum
mechanics there for they can solve higher
class problems.
Quantum Annealing, How does it work?
Like I mentioned before quantum annealing
used the nature characters of quantum
physics for qubits to find the lower energy
state in order to determine the result.
So qubit will start at a superposition, and
when annealing finishes they will be in one
of 2 basic states(spin up , spin down)
because super position can’t be measured.
Quantum Annealing, How does it work?
With the energy diagram on the right we
can see that when the annealing is finished
we will get a diagram which is know as
“Double-well potential” that will give us a
low energy state. But with all variable being
the same the probability of spin up and
spin down of the qubits are the same so we
can’t solve any problem, there for we have
to programme the quantum computer.
So in order to control the probability of a
qubit falling into one state or another we
can apply an external magnetic field to the
qubit aka ”bias” to influence the qubit to go
to the lower energy valley.
Quantum Annealing, How does it work?
Like I mentioned in the introduction of
quantum computing the true power of
quantum computer shows when you have
quantum entanglement because the bits of
information is growing exponential.
Now we are talking about how to use
quantum entanglement in Quantum
Annealing, so when qubits are entangled
they are concerted as one object but
because the number of bit or state is
increased exponential so the number of
state is 2N qubits so that’s why it’s faster.
Quantum Annealing, How does it work?
So in quantum annealing you will setup a
problem for the quantum annealing to solve
with the entanglement and the bias to
create a energy terrain map which quantum
annealing process will be able to find the
lowest energy state possible and that will be
one of the best solution for your problem
and the end result of the solution will be in
one of two basic states, it will be measured
and transferred to a classical computer and
translate to these programme the
programmer is using and provide the
solution in binary format.
Universal Gate Model Quantum Computing
In gate model quantum computing it tries to
control the evolution of qubits instead of
using the nature of the qubits.
But a quantum system is very delicate and
hard to work with so the gate model
quantum computers are not able to scale up
and put in real world use, in theory if they
are scaled up they will be way more
powerful than a Quantum Annealing
computer every will by using algorithms such
as Shor's algorithm and Grover's algorithm.
But on the other hand D-Wave’s 2000Q
system already has 2000 qubits and it has
been in real world use for a few years. And
they have a 16 qubit chip since 2007.
On the other hand the world’s first
Universal Quantum Computer service is
just rolling out this year with IBM Q
with 5 Qubits, they are getting a 16
qubit one…..(Gate Model Quantum
Computing started development before
quantum annealing was devolved.
Types of Universal Gate Model Quantum
Computing:
• Measurement Based Quantum Computing
• Adiabatic Quantum Computing
• Topological Quantum Computing
Measurement Based Quantum Computing
Measurement based quantum computer is a method of
quantum computing that first prepares an entangled
resource state. then performs single qubit
measurements on it. It is "one-way" because the
resource state is destroyed by the measurements. ( This
is a type of quantum computing that I can’t find much
information on and all the information I can find are all
from at least 6 years ago, I believe it’s no longer a main
stream technology).
Adiabatic quantum computation
Adiabatic quantum computing is a type a quantum
computing which is closely related to quantum
annealing and part of the community believe it can
be a sub class of quantum annealing there is a very
heated debate around Adiabatic quantum computing
and Quantum Annealing.
In simply terms Adiabatic Quantum computation is a
computational model which is more focus on
experimental designs and the optimization of the
algorithms.
Topological Quantum Computing
Topological Quantum Computer is a very unique type of
quantum computer, because it’s completely theoretical and
it requires some 2D quasiparticle which is a particle inside
matter which many scientist are not sure that it exists. But
Microsoft decide to build their Universal Quantum
Computer with this quantum computation model.
The main pro of a Topological Quantum Computer is it’s
resentence to the outside environment. Because Qubits
only need a very small energy to change it’s state so it has
to be kept at temperature as close to absolute zero as
possible and without any unwanted radiation. But with
Topological Quantum Computer we can make Quantum
Computer way more robust.
The Future Of Quantum Computing and conclusion
The future of quantum computing is bright, But today is not the day that quantum computer will
replace the classical computers. With the most “client friendly” option D-Wave computer still needs
an extensive support system to keep it running. But in the long run with the superior efficiency and
the reduced cost quantum computer can replace big super computers and maybe one day it can
replace our personal computer.
In my opinion universal quantum computer will be the main stream of quantum computer in the
future if scientist can find a method of scaling up it will have way more potential than a Annealing
Quantum Computer is capable of. It can solve a class of problem that can’t be solve by classical
computer, instead annealing quantum computer can just solve classical computing problem way
faster.
There are still a lots of challengers to let quantum computer compete with classical computers such
as the very low temperature and low radiation environment it have to be in and one day it will face
the quantum tunneling issue which classical computer is facing right now but one day it might
replace the computer as we know are.
Citation
Reference
Inc, D.-W. S. (2017, January 11). Welcome to the future. Retrieved January 13, 2017, from http://www.dwavesys.com/
Qubit (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Qubit
Schrödinger’s cat (2017). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Schr%C3%B6dinger’s_cat
Two-state quantum system (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Two-state_quantum_system
Unitary transformation (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Unitary_transformation
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Retrieved January 13, 2017, from https://en.wikipedia.org/wiki/Quantum_computing
Citations, Quotes & Annotations
Inc, D.-W. S. (2017, January 11). Welcome to the future. Retrieved January 13, 2017, from http://www.dwavesys.com/
(Inc, 2017)
Qubit (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Qubit
(“Qubit,” 2016)
Schrödinger’s cat (2017). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Schr%C3%B6dinger’s_cat
(“Schrödinger’s cat,” 2017)
Two-state quantum system (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Two-state_quantum_system
(“Two-state quantum system,” 2016)
Unitary transformation (2016). . In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Unitary_transformation
(“Unitary transformation,” 2016)
Retrieved January 13, 2017, from https://en.wikipedia.org/wiki/Bloch_sphere
([CSL STYLE ERROR: reference with no printed form.])
Retrieved January 13, 2017, from https://en.wikipedia.org/wiki/Quantum_superposition
([CSL STYLE ERROR: reference with no printed form.])
Retrieved January 13, 2017, from https://en.wikipedia.org/wiki/Quantum_computing
([CSL STYLE ERROR: reference with no printed form.])
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(2veritasium, 2013a)
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(2veritasium, 2013b)
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(Google, 2013)
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(Techquickie, 2014)
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(Veritasium, 2013a)
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(Veritasium, 2013b)
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Adams, A., Evans, M., & Zwiebach, B. (2001). Quantum physics I. Retrieved January 13, 2017, from
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(Adams, Evans, & Zwiebach, 2001)
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