1. From Bits to Qubits Wayne Viers and Josh Lamkins
Quantum Computing
From Bits to Qubits
Wayne Viers and Josh Lamkins

2. What is Quantum Computing?
Quantum computing is the field of research associated with building a quantum computer and creating algorithms to harness its power.
Building a quantum computer
is not as simple as connecting
processors and memory like
a normal computer.

3. Types of Quantum Computers
1) Gate Model Quantum Computer
Based on a very familiar approach that traditional computers use.
Gate model quantum computing creates quantum equivalents of digital logic gates – and puts these gates together to build a quantum computer.
2) Adiabatic Quantum Computer
Relatively robust against environmental interference.
Allows scientists to leverage existing superconducting integrated circuit technology
Built using macroscopic-sized qubits fabricated using semiconductor fabrication techniques.

4. Gate Model Quantum Computer
The Good News:
Crucial for improving our understanding of quantum computing
Helps in pushing research forward.
The Bad News:
Very difficult to build and scale
They are extremely susceptible to environmental factors
Difficult to control and correct for errors
Despite many years of research, there has been very slow progress made toward the development of anything near commercially useful

5. Adiabatic Quantum Computing
Adiabatic Quantum computers operate in extreme environments.
Processor is placed in dilution refrigerator
Cooled to 150x colder than interstellar space (0.02 Kelvin)
Shielded to 50,000× less than Earth’s magnetic field
Placed in a high vacuum: pressure is 10 billion times lower than atmospheric pressure

6. What is a Bit?
A bit is the basic unit of information in computing and digital communications.
Represented in a computer as an electrical signal.
The most common representation of these values are 0 and 1.

7. What is a QuBit? A unit of Quantum information
Qubits are often made of subatomic particles
Photons
Coherent State of Light
Electrons
Nucleus
Optical Lattices
Josephson Junction
Singularly Charged Quantum Dot Pair
Quantum Dot

8. Representation of a QuBit
For qubits implemented by electrons, the state is represented by the direction of spin 1

9. Quantum Superposition
The fundamental principle of quantum mechanics
A physical system - such as an electron - exists partly in all its particular theoretically possible states simultaneously
When measured or observed, it gives a result corresponding to only one of the possible configurations

10. Quantum Parallel Processing
In classical computers, parallel computing is performed by having several processors linked together, so that each processor performs one computation while the other processors are performing other computations.
In a quantum computer, a single quantum processor is able to perform multiple computations on its own by utilizing the fact that the qubit (or quantum bit of information) exists in multiple states simultaneously. This gives a quantum computer much greater raw computation ability than a traditional computer (to).
Turn it over to Wayne to speak more about the practical applications of Quantum Computers.

11. Requirements for a Working QC
It must be scalable: it needs a set of qubits that can be added to indefinitely.
It must be possible to set all of the qubits to a simple initial state, such as all 0.
The interactions between qubits must be controllable enough to make quantum logic gates.
To perform operations using these gates, the decoherence times must be much longer than the gate-operation time (typically milliseconds to seconds).
There must be some readout capability.
To link up the computer's circuitry, it must be possible to convert memory qubits into processing qubits, and vice versa.
It must be possible to move processing qubits accurately between specified locations.

12. Deterministic vs. Probabilistic
Deterministic Algorithm
Given a particular input, a deterministic algorithm will always produce the same output, with the underlying machine always passing through the same sequence of states
Probabilistic Algorithm
Any algorithm that works for all practical purposes but has a theoretical chance of being wrong
Quantum computers are probabilistic because the final answer is a collapse of all of the quantum states
One qubit can collapse to any single value from its supposition

13. Problems/Areas of Improvement
Observer Effect
Qubits cannot be observed without destroying their state.
Decoherence
Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way.
Must go to great lengths to create interference free environment → control pressure, temperature, electromagnetic waves etc.

14. Decoherence

15. Uses for Quantum Computers
Could provide quadratic speedup for searching an unordered database using Grover’s algorithm
Shor’s algorithm
-O((log N)^3) time integer factorization
Could be used to break public key cryptography like RSA

16. Current Developments Quantum Gate Arrays Hadamard Gate
A series of linear transformations performed on qubits to make an algorithm
Similar to the structure of a normal computer with logic gates
allows for the transfer of energy between qubits
External forces can easily disrupt these exchanges
Hadamard Gate

17. Current Developments One-way quantum computer
A gate-model quantum computer using quantum gates
Sets up initial entangled resource state pertaining to problem
Applies logic gates then takes a measurement, destroying the resource state
Has a high amount of error, many trials required

18. Current Developments Adiabatic quantum computing
A series of qubits kept at a very low ground state by cooling them to near zero degrees Kelvin.
A specific transverse field is applied to the qubits that cause their values to fluctuate.
After the transverse field is switched off, the solution is measured.
Used in D-Wave

19. Current Developments
“a quantum adiabatic computer does a rapid global search. It starts with the analogue of tipping water onto a flat landscape — a state in which the qubits are in a perfect quantum superposition of zeroes and ones — then lets the mountains rise slowly, so that the water naturally pools in the best solutions.”

20. Current Developments Topological Quantum Computer
Theoretical quantum computer that employs two dimensional quasiparticles called anyons whose trajectories in space time cross one another to form braids in three dimensional spacetime
These braids form logic gates
The braids are much more stable than trapped quantum particles
May be created using semiconductor plates at a temperature near absolute zero and subjected to strong magnetic fields

21. Questions?