Quantum Computing

Question 1

What is superposition?

Answer 1

Superposition recognizes that position and momentum are not fixed for subatomic particles, as predicted by classical physical rules. Thus, a qubit can exist anywhere between 0 and 1 QC is basically is a classical information system based on `quantum mechanics’ containing the largest information unit with a qubit [5].

Question 2

What is entanglement?

Answer 2

Quantum entanglement is the state where two systems are so strongly correlated that gaining information about one system will give immediate information about the other no matter how far apart these systems are.

Entanglement is a combination of qubits that cannot explain how the system will work by looking at each qubit.
No longer possible to measure all the individual qubits – must be measured as a set.

In quantum computers, changing the state of an entangled qubit will change the state of the paired qubit immediately. Therefore, entanglement improves the processing speed of quantum computers. Doubling the number of qubits will not necessarily double the number of processes since processing one qubit will reveal information about multiple qubits (i.e. the entangled qubits). According to research, quantum entanglement is necessary for a quantum algorithm to offer an exponential speed-up over classical computations.

Question 3

What happens when you view a quibit?

Answer 3

It collapses to a value.

Question 4

What is the Born Rule?

Answer 4

The Born Rule states it needs to convert quantum amplitudes does not give us probability and that if we observe a quantum system it will behave as if the quantum amplitude of its quantum amplitudes are squared.

Question 5

What is a Josephson Junction?

Answer 5

The Josephson tunnel junction consists of two superconductors separated by a thin insulating barrier through which Cooper pairs of electrons can tunnel coherently. For each superconductor, the density of Cooper pairs and their common phase describe its macroscopic quantum state.

A Josephson junction is a small, very sensitive circuit that combines supercurrents with the quantum phenomena of tunneling of coupled electrons which lead to a current flowing in the circuit.

Question 6

Explain some attributes of logic gates?

Answer 6

Quantum logic gates are circuits working on one or more than one qubit. Quantum logic gates are effectively described using matrices.
Apply logic gate equals the state vector multiplied by the matrix of the logic gate.

Question 7

Describe the differences between quantum and classical computation.

Answer 7

The big difference compared to a classical computer is that a quantum computer is following a different rule set. It’s not using zeros and ones like classical computers are – bits and bytes – but it is actually able to work with something called qubits.

Question 8

Discern potential performance gains of quantum vs. classical algorithms.

Answer 8

Quantum computing is a new generation of technology that involves a type of computer 158 million times faster than the most sophisticated supercomputer we have in the world today. It is a device so powerful that it could do in four minutes what it would take a traditional supercomputer 10,000 years to accomplish.

Question 9

Assess the business applications of quantum computation

Answer 9

7 ways quantum computing can help businesses
Cryptography. The most common area people associate quantum computing with is advanced cryptography. …
Aviation
Data Analytics
Forecasting
Pattern Matching
Medical Research
Self-Driving Cars

Question 10

Understand engineering challenges currently faced by developers of quantum computers

Question 11

What is supercondense coding?

Answer 11

Superdense coding
In simple words, superdense coding is the process of transporting 2 classical bits of information using 1 entangled qubit. Superdense coding can:

Allow user to send ahead of time half of what will be needed to reconstruct a classical message ahead of time, which let’s the user transmit at double speed until the pre-delivered qubits run out.
Convert high-latency bandwidth into low-latency bandwidth by sending half of the information over the high latency channel to support the information coming over the low latency channel.
Double classical capacity in one direction of a two-way quantum channel (e.g. converting a 2-way quantum channel with bandwidth B (in both directions) into a one-way classical channel with bandwidth 2B).

Question 12

Explain key Exchange in a quantum state.

Answer 12

Cryptography is the process of exchanging information between two parties using an encrypted code and a deciphering key to decrypt the message.

The key to cryptography is to provide a secure channel between 2 parties. Entanglement enables that. If two systems are purely entangled that means they are correlated with each other (i.e. when one changes, the other also changes) and no third party shares this correlation. Additionally, quantum cryptography benefits from the no-cloning theorem which states that: “it is impossible to create an independent and identical copy of an arbitrary unknown quantum state”. Therefore, it is theoretically impossible to copy data encoded in a quantum state.

Question 13

What is quantum teleportation?

Answer 13

Quantum teleportation is also the process of exchanging quantum information such as photons, atoms, electrons, and superconducting circuits between two parties. Research suggests that teleportation allows QCs to work in parallel and use less electricity reducing the power consumption up to 100 to 1000 times.

The difference between quantum teleportation and quantum cryptography is:

quantum teleportation exchanges “quantum” information over a classical channel
quantum cryptography exchanges “classical” information over a quantum channel
Challenges that currently face quantum teleportation are:

the volume of teleported information
the amount of quantum information shared between the sender and receiver has before teleportation.
The sender should have one of the qubits of the pair and the receiver the other qubit of the pair
The strength of prior correlation between the sender and the receiver qubits increases the capacity of a quantum channel
teleportation circuit noise acting on the quantum channels

Question 14

Discuss quantum programming languages.

Answer 14

Quantum programming languages are the foundations to interpret ideas into instructions to be carried out by a quantum computer. According to Nature Reviews, quantum programming languages are used to:

manage existing physical devices
predict quantum algorithms’ execution costs on possible devices
examine quantum computing concepts (qubits, superposition, entanglement)
test and verify quantum algorithms and their implementations
Current quantum programming languages and compilers are mainly focused on optimizing low-level circuits consisting of quantum gates. Quantum gates are the building blocks of quantum circuits. They are similar to reversible logic gates such as Fredkin gate, Toffoli gate, interaction gate, and switch gate. However, the smallest classical reversible gate has to use three bits, whereas the smallest quantum gate needs to use only two bits.

Question 15

Discuss imperative programming languages.

Answer 15

Imperative programming languages consist of step-by-step instructions to be performed in order to accomplish the desired result. In classical computers imperative languages include C, JavaScript, Pascal, Python, etc. The most popular quantum imperative languages are:

QCL: Quantum Computing Language, one of the first implemented quantum programming languages. It resembles C language in regards of syntax and data types.
QMASM: Quantum Macro Assembler, published in 2016. It is a low-level language specific to quantum annealing. The significance of QMASM is that it relieves the programmer from having to know system-specific hardware details while still allowing programs to be expressed at a low level of abstraction.
Silq is originally published in 2020. Silq is a high-level programming language written in D language which has 482 stars and 10 contributors on github and is regularly updated as of 2021.
Other imperative Q languages include Quantum pseudocode, Q|SI>, Q language, qGCL, and Scaffold.

Question 16

Explain Functional languages.

Answer 16

Functional languages don’t rely on step-by-step instructions, instead they depend on mathematical functions which means inputs are converted into output using mathematical transformations. Functional languages are less popular than imperative ones because they don’t support flow controls (e.g. loop statements) or conditionals (e.g. if/else statements). However, due to these features, they benefit from:

Fewer bugs
Programmers writing and reviewing a functional code claim to spot errors more easily because there are fewer places for surprising behavior to hide
Functional errors are reported to be easier to fix
Nested functions
Lazy evaluation:
delays the evaluation of an expression until its value is needed
avoids repeated evaluations
Top functional languages for quantum computers are:

QML: published in 2007, a Haskell-like quantum programming language based on strict linear logic. It can integrate reversible and irreversible quantum computations
Quantum Lambda Calculus: it is based on classical lambda calculus introduced in 1930 and was first defined for quantum calculations in 1996. It uses high-order functions (λx.x^3) Therefore, it is stronger than the standard quantum computational models, such as quantum Turing machine or the quantum circuit model.
QFC and QPL: Semantically QFC and QPL are equivalent. However, in QFC, quantum programs are represented using flowchart syntax, but in QPL syntactic structure of quantum programs are represented using textual representations.
Other functional languages include LIQUi|> and Quipper.

Question 17

Identify Multi-paradigm languages.

Answer 17

There are also multi-paradigm languages that are domain-specific such as Q# for Microsoft and Strawberry Fields for XanduAI.

Question 18

Discuss Quantum programming

Answer 18

The purpose of programming quantum computers is to solve quantum physics’ problems. Quantum algorithms that can be programmed include:

Algebra and number theory algorithms, such as factoring and Gauss sums
Approximations and simulations, such as quantum simulation, zeta functions, and knot invariants
Machine learning algorithms, such as clustering, binary classification, and training neural networks
More quantum algorithms that can be programmed are mentioned in the “Quantum Algorithm Zoo” by Stephen Jordan of the National Institutes of Standards and Technology.

Question 19

Explain the challenges in quantum programming.

Answer 19

Challenges in quantum programming
The difficulties in quantum computer programming arise from:

Difficulties in formulating universal QC languages
Incompleteness and hidden variables in quantum mechanics
Quantum computers are still in their infancy working on <100 Qubits, therefore, not strong enough to run complex quantum algorithms.
However, the availability of open source SDKs is allowing communities to find solutions for programming challenges and find more practical applications for quantum computing.

Question 20

Explain photonics.

Answer 20

Photonics
Photons have a natural isolation property due to their weak interactions with the surrounding environment, which makes them a great candidate to carry information, represent qubits, and operate at room temperature. Another advantage is that photonic quantum computers can be integrated into existing fiber optic-based telecommunications infrastructure.

However, one of the challenges that face photonic quantum computing is the limitations in fault tolerance and error correction.

Current companies developing photonic quantum computing technology include PsiQuantum, Xanadu, and the Amazon Quantum Solutions Lab.

Question 21

Explain trapped ions.

Answer 21

Trapped ions
Quantum hardware that uses trapped ion qubits typically rely upon microwave or optical signals transmitted through free space or waveguides and delivered to the location of the qubits. Current QC prototypes of trapped-ion consist of a chain of 5 to 20 static ions in a single potential well. Challenges that face trapped-ion systems are:

the difficulty of isolating individual ion motions as chain length increases
the number of ions one can individually address with gate laser beams
measuring individual qubits
Current companies that work on ion-trapped quantum technologies include Honeywell and IonQ,

Question 22

How does a developer interact with the quantum computer?

Answer 22

To program a quantum computer, the programmer will send the algorithms via a host system, typically called “host processor”. A host processor is a classical computer which has a high bandwidth connection to the QCU. The host runs a conventional operating system to allow the user interaction with the quantum processor.

Question 23

How do wavefunctions work in a quantum system?

Answer 23

In a Quantum System, wavefunctions are added together. You can have constructive interference and destructive interference.

Question 24

What is quantum complexity theory?

Answer 24

Quantum Complexity Theory – sourcing in bins how well they run on computer. How hard is it to solve with a classical computer (P box) and anything out. BQP categorization, quantum will be able to process efficiently.

Question 25

What is the halting problem?

Answer 25

In 1936, Alan Turing showed that the Halting Problem – algorithmically deciding whether a computer program halts or loops forever – cannot be solved. Modern computer science was born. Its success made the impression that soon all practical problems would yield to the tremendous power of the computer.

Question 26

What are the models of quantum computing?

Answer 26

Circuit or Gate Model – entangled qubits that can operate on by the gates. The quantum algorithm identifies the multiple operations (gates) on each qubit.
* One Way Model (Measurement Based) – setting up a qubits
* Adiabatic – advantage behavior of moving toward minimum energy state. Poses problems is that the minimum energy state is the correct answer. Start off with a flat landscape then add the energy landscape of the problem. Most likely to get the correct answer. Hamiltonis and Eichen states.

Question 27

What are hamiltonians?

Answer 27

Hamiltonian of a system is an operator corresponding to the total energy of that system, including both kinetic energy and potential energy.

This was the original problem suggested by Feynman where quantum computers could reasonably do better than classical computers, as a quantum computer can naturally represent the unitary evolution.

This raises another question: Why would one want to do Hamiltonian simulation? There are many reasons, but generally, if we can efficiently do Hamiltonian simulation (for instance on a quantum computer), then we can study directly how structures at the smallest scales (such as atoms or molecules, but also certain properties of Quantum Field Theory) interact and evolve. This is important to the field of quantum chemistry where one for instance wants to know how the physical structure of a molecule evolves trough time. At a larger scale it could also prove useful to for instance pharmaceutical companies who can then directly simulate the effect of their drugs on the cells in our bodies (although this is very much pie in the sky at the moment).

Question 28

What are eigenstates?

Answer 28

An eigenstate is the measured state of some object possessing quantifiable characteristics such as position, momentum, etc.

What are eigenstates of a quantum system?
In quantum mechanics, a measurement of an observable yields a value, called an eigenvalue of the observable. Right after the measurement, the state of the system is an eigenstate of the observable, which means that the value of the observable is exactly known.

Question 29

Universal Quantum Computing scheme – can simulate all other quantum systems

Answer 29

• Quantum Annealing – not universal quantum. Does not have the full degrees of freedom to explain each option
• Topologic Quantum Computing – Majorana Zero-Mode Quasi-Particle, Non-abelian anyon. Quasi-particles are created from collective behavior of multiple particles. (Electron Hole – can treat like a particle).
• Majorana Zero Mode Quasi Particles (MZMS) – not sure if they have been observed. Quasi-particles are more stable because they are made of parts of that are physical separated. Protected because it take energy to break them apart. Protected by energy gap.
• Main source of failure of quantum computing is noise – noise can be heat, vibration, rogue particles, signals.
• Obstacles – hard to control
  o Outside interference Decoherence

Question 30

Physical Implementation of Quantum Computing

Answer 30

• Superconducting Quantum Computers using superconducting wires with Joseph’s junction to break. Transmon qubit, pairs (Cooper pairs) of electric charge moving over the junction..
• Magnetic flux in a loop of wire (Flux qubit)
• Phase qubit phase across the wire
• Quantum Dot Quantum or Silicon Spin QU. Qubits are made of electrons – spin or charge. (quantum dot). Control with microwaves or voltages or magnetic fields. Made of silicon, gallium, arsenide, silicon
• Linear Optional Quantum computers – using photons of lights using waveplates, mirrors, and interferometers. Made into integrated photonic chips. The path the photon takes, or a number of photons.
• Trapped Ion Quantum Computers. Ions missing electrons are trapped in magnetic fields. Controls and read by laser (read energy level)
• Color Centre Quantum Computers – atoms are embedded in gape nitrogen embedded in diamond or silicon carbide. Nuclear spins
• Neutral atoms in optical Lattices – capturing neutral atoms in an optical lattice, Cooled down to a millionth of a kelvin, energy level of atoms. Controls with lasers. Cesium is an example
• Other ones not popular include
  o Electron On Helium Qubit
  o Cavity Quantum Electrodynamics
  o Magnetic Molecule Molecular Spings
  o Nuclear Magnetic Resonance.

Question 31

Please identify what companies working on quantum computing.

Answer 31

IBM Superconducting Qubits biggest 65 qubits. 1000 by 2023 (5 to 16 qubit machines can be used)
Rigetti Superconducting Qubits
D Wave Sells commercially available 5600 qubits, cannot be compared. Solving for certain problems.
Google Superconducting Qubits – 53 qubits
IONQ 32 trapped ions in a chain
Honeywell Trapped ION computing. Longer coherence time, can interact with more neighbors. Disadvantages slower to react, Quantum volume – factors errors, cross talk, etc 64
* IonQ (Trapped Ion Computing Company) …
* Alpine Quantum Technologies. …
* Oxford Ionics (Trapped Ion Company) …
* EleQtron.
PSIQantum Photonic Quantum Computing – say they can scale up.
Xanadu Photonic Quantum Computing (can be operated at room temperature, last longer), disadvantages – systems become large
No topological quantum computers exist