Questions tagged [computational-models]
For questions on theoretical models of quantum computations. Such models may be realistically 'build' in real machines, but not necessarily.
54
questions
63
votes
7
answers
6k
views
What are the models of quantum computation?
It seems that quantum computing is often taken to mean the quantum circuit method of computation, where a register of qubits is acted on by a circuit of quantum gates and measured at the output (and ...
- 1,985
28
votes
2
answers
5k
views
What is the difference between quantum annealing and adiabatic quantum computation models?
From what I understood, there seems to be a difference between quantum annealing and adiabatic quantum computation models but the only thing I found on this subject implies some strange results (see ...
- 4,927
26
votes
2
answers
2k
views
Why can't quantum annealing be described by a gate model?
This is a question I was inspired to ask based on this question, which notes that quantum annealing is an entirely different model for computation than the usual circuit model. I've heard this before, ...
- 1,087
19
votes
2
answers
2k
views
How does topological quantum computing differ from other models of quantum computing?
I've heard the term Topological Quantum Computer a few times now and know that it is equivalent to quantum computers using circuits with respect to some polynomial-time reduction.
However, it is ...
- 512
17
votes
2
answers
700
views
In a Quantum Turing Machine, how is the decision to move along the memory tape made?
Let, for a Quantum Turing machine (QTM), the state set be $Q$, and the alphabet of symbols be $\sum=\{0,1\}$, which appear at the tape head. Then, as per my understanding, at any given time while the ...
- 223
13
votes
4
answers
756
views
Who built the first quantum computer using at least two qubits?
In my previous question I asked who invented a quantum computer using qubits.
As a follow-up to this question I want to ask who built the first quantum computer using at least two qubits.
During my ...
- 1,047
13
votes
0
answers
262
views
Does the Curry-Howard correspondence have a quantum-specific type system?
In Wikipedia we can read that
the Curry–Howard correspondence is a correspondence between formal proof calculi and type systems for models of computation. In particular, it splits into two ...
- 754
10
votes
3
answers
868
views
What is the simplest algorithm to demonstrate intuitively quantum speed-up?
What's the simplest algorithm (like Deutsch's algorithm and Grover's Algorithm) for intuitively demonstrating quantum speed-up? And can this algorithm be explained intuitively?
Ideally this would be ...
- 1,129
9
votes
1
answer
206
views
What good references would you recommend to understand the (continuous-variable) CV model of computation?
If you have good references about the CV model that are understandable from a computer science background, that would be great. If they include numerical examples, that would even be better.
- 4,754
9
votes
1
answer
189
views
Where can I find example circuits to learn from?
I'm relatively new to quantum computing and my goal is to learn how to implement algorithms that I read in papers. While I have found many circuit snippets I have yet to find a repository of examples ...
8
votes
1
answer
2k
views
What are the fundamental differences between trapped ion quantum computers and other architectures?
There are many different ways to build quantum computers, such as superconducting qubits, quantum dots, and ion traps.
What I would like to understand is why some universities and research ...
- 203
8
votes
1
answer
115
views
Correspondence between the Topological model and Quantum Circuit model
For example, given the $R$ & $F$ gates and Toric codes for a given problem, how to convert this code into the conventional circuit model and vice versa.
From the literature developed, it seems ...
user5438
7
votes
2
answers
3k
views
What are the pros/cons of Trapped Ion Qubits, Superconducting Qubits and Si Spin Qubits?
Among available qubit technologies for universal quantum computing these 3 come up as promising. NV centers and Majorana qubits also underway but relatively new.
I find superconducting qubits and ...
- 355
7
votes
1
answer
266
views
Are ladder operators ever extensively used in any model of quantum computation?
Computer scientists and others who are interested in learning more about quantum computation might be exposed, or re-exposed, to various concepts and classes of matrices from linear algebra. For ...
- 12.2k
6
votes
2
answers
285
views
Anyon alternatives in topological quantum computing
A topological quantum computer is a theoretical quantum computer that employs two-dimensional quasiparticles called anyons. -Wikipedia
Are there other instances of topological quantum computing ...
- 3,302
6
votes
2
answers
1k
views
What exactly are "quantum rotors"?
The Wikipedia entry on the subject is rather short. I am also curious about generalizations of quantum rotors in n-dimensions. An introductory explanation with at least one resource for further ...
- 3,302
5
votes
3
answers
1k
views
Is it possible to simulate a quantum computer in Virtual Reality? If yes, how?
There have been a couple of simulations already made and I recently saw this high performance, hardware accelerated quantum computer simulator QCGPU and started to wonder about how to simulate quantum ...
- 185
5
votes
1
answer
981
views
What is entropy quantum computing?
Recently there is news concerning some computational breakthroughs by using so-called "entropy quantum computing":
https://thequantuminsider.com/2022/07/20/qci-solves-3854-variable-problem-...
- 51
5
votes
1
answer
154
views
Which theoretical models for quantum computing are polynomial-time equivalent? [duplicate]
There are different theoretical models for quantum computing like the circuit model or the model of adiabatic quantum computers.
Between which of these models exist polynomial-time reductions?
Note ...
- 512
5
votes
1
answer
163
views
Where is entanglement present and absent in the one clean qubit model of computation?
Based on my limited and poor understanding, a quantum circuit in the "one clean qubit" model of quantum computation generally acts on a single pure (clean) qubit tensored with $n-1$ qubits ...
- 12.2k
5
votes
1
answer
193
views
What is continuous quantum register and how it relates to qubits?
I would like to understand what is a continuous quantum register.
I know the direct definition is a quantum register that stores a real number defined by an observable with a spectrum consisting of $\...
- 4,754
4
votes
1
answer
447
views
Proof that any unitary can be written as $U=e^{-iH}$ with $H$ Hamiltonian with bounded norm
I am looking for a proof that any unitary matrix can be written as:
$$U = e^{-iH}$$
where $H$ is some Hamiltonian with bounded norm. That is $$||H||_{2} = O(1).$$
- 1,313
4
votes
2
answers
493
views
Is quantum parallel search impossible?
Scott Aaronson's blog notably states:
Quantum computers would not solve hard search problems
instantaneously by simply trying all the possible solutions at once.
Is this a statement of a law, as ...
- 1,340
4
votes
2
answers
231
views
Quantum computing concepts
I am trying to develop a feel for quantum computing at a basic level. I would very much appreciate someone will take a look at the statement below and fix it, since I assume it needs fixing.
“...
- 221
4
votes
1
answer
295
views
Chrononic Computing (Time Evolution Systems)
In a recent question about quantum speed-up @DaftWullie says:
My research, for example, is very much about "how do we design Hamiltonians $H$ so that their time evolution $e^{-iHt_0}$ creates ...
- 3,302
4
votes
1
answer
541
views
Minimum number of 2-qubit gates required to implement a Toffoli gate
I'm trying to design a quantum circuit that has an output that is closest to a CCNOT gate with no more than four 2-qubit gates (but I can use additional single qubit gates).
A lot of resources/papers ...
- 41
4
votes
1
answer
154
views
Why do quantum computation models based on open quantum systems receive so little attention?
In almost all research on (universal) quantum computation the common models assumed from the outset are either the quantum circuit model with unitary gates, the measurement-based one-way model or the ...
- 223
4
votes
0
answers
75
views
Does there exist a one-way quantum computer?
I'm wondering if we have managed to create a experimental version of a one-way computer and if so is there one available to "play with" as it is the case with circuit models which are ...
- 75
4
votes
0
answers
69
views
What type of tasks it is possible to solve on a quantum simulator?
In this article, the author claimed that researches from Harvard and MIT created 256 qubits quantum simulator. However, we are not talking about piece of software on a classical computer but actual ...
- 14.1k
4
votes
0
answers
61
views
Modeling building blocks for quantum computation
If I would design library for quantum computation I would naively consider a sequences of entangled qudits with unit length as a building blocks. I.e., unit length elements from $$\mathbb{C}^{d_{1}}\...
- 269
3
votes
1
answer
1k
views
Do quantum loops exist?
I was checking the book from Nielsen and Cheng and they mention in chapter 1, page 23, that quantum circuits don't have loops:
"There are a few features allowed in classical circuits that are not ...
- 209
3
votes
1
answer
175
views
Aren't reversible logic gates a necessity for efficiently executing quantum algorithms?
The Wikipedia article on logical reversibility says:
...reversible logic gates offered practical improvements of
bit-manipulation transforms in cryptography and computer graphics.
But I guess ...
- 17.5k
3
votes
1
answer
429
views
Applications of Quantum Computing to Economics
I have recently been interested in the field of 'Econophysics' which as I understand it is the practice of basically applying results of physics in areas such as non-linear dynamics and stochastic ...
3
votes
1
answer
38
views
Why does the condition $\langle \varphi _k\left( t \right) |\dot{\varphi}_l\left( t \right) \rangle =0$ called parallel transport condition?
I'm reading this paper about nonadiabatic holonomic quantum computation and met the condition eq.(2) states that $\langle \varphi _k\left( t \right) |\dot{\varphi}_l\left( t \right) \rangle =0$ is the ...
- 695
3
votes
0
answers
119
views
Why is the resource theory approach used in quantum information processing? [closed]
What are the advantages and applications of using the resource theory approach in QIP ? What specific problems can be solved using in particular this approach ?
- 31
2
votes
1
answer
230
views
What does "large-scale universal quantum computation" mean?
I was reading this lecture notes by Sevag Gharibian. He mentioned the following statement:
Large-scale universal quantum computer can be built.
I do understand what quantum computer is, but I don't ...
- 377
2
votes
1
answer
1k
views
How to measure one of the qubits in a two-qubit register?
How do I measure the first qubit of an entangled vector, say
\begin{pmatrix}
1 \\
-1 \\
0 \\
0 \\
\end{pmatrix}
is what I get on the end of Deutsch's algorithm. If I get it right, I should now ...
- 107
2
votes
1
answer
114
views
Quantum circuits, quantum Turing machine and universal quantum computer-comparing different models of quantum computations
Forgive me if this question was already asked somewhere on this site-I haven't found it but it is possible that I've overlooked it. So basically, I would like to summarize different notions of quantum ...
- 133
2
votes
1
answer
722
views
Pennylane: take qml.state of one function and use it as the initialization for another
In Pennylane, I created a function to set the initial parameters of my qubit, and then called qml.state() to return the output. I now want to feed this initialization into another circuit, but I'm not ...
- 33
1
vote
1
answer
141
views
PreciseQMA = PreciseBQP gives PP = PSPACE
$\text{PreciseBQP}$ is defined as $\text{BQP}$ with inverse exponentially close completeness and soundness bounds (for a better definition, see Section 3.1 here, in the paper by Gharibian et al). ...
- 1,313
1
vote
1
answer
99
views
IBM Q Experience - Can it be used draw out ML inferences? [closed]
Are there Quantum-enhanced Machine Learning algorithms that can be implemented via Qiskit in IBM Q Experience and obtain valuable inferences faster than their classical counterparts from datasets of ...
- 23
1
vote
1
answer
110
views
Is there an inherent difference in need for error correction between quantum annealing and gate based methods?
When I read about computing using gate based methods, I mainly read about the difficulties with error rates, circuit depth (and connectivity) and not enough qubits.
With computing using quantum ...
1
vote
0
answers
22
views
Quantum code for Substitution Box
How to write quantum code(qiskit) for n-bit Substitution Box with minimum number of gate and qubit.
1
vote
0
answers
32
views
How to show that controlled-square-root-of-Z gates and T gates generate all IQP circuits?
The class of instantaneous quantum polynomial (IQP) circuits is an interesting restricted model of quantum computation - circuits running according to the model likely cannot achieve the full scope of ...
- 12.2k
1
vote
0
answers
66
views
What's the difference between Superconductor, Photonics, and Nuclear Magnetic Resonance implementation of the physical QC?
I'm a bit new to Quantum Computing and I wonder why organisations are using different physical architecture.
I realise that any physical implementation can be valid as long as it uses the fundamentals ...
- 247
1
vote
0
answers
55
views
How to simulate $H(\theta) = B(\sin\theta S_1^x +\cos\theta S_1^z +\sin\theta S_2^x +\cos\theta S_2^z)+aS_2^zI_z$ on IBM Qiskit
I am trying to simulate this Hamiltonian on IBM Qiskit, for varying values of $\theta$:
$H(\theta) = B(\sin\theta S_1^x +\cos\theta S_1^z +\sin\theta S_2^x +\cos\theta S_2^z)+aS_2^zI_z$
Where S is ...
1
vote
0
answers
26
views
What is the relation between the database made up of N elements and the index made up of a string length n in the query model?
I am working on a circuit model that contains a blackbox (query) and do not understand the relationship between what is in the black box and the way we get out the value of the element we index. The ...
1
vote
0
answers
85
views
Screening procedure in an iterative qubit coupled cluster (iQCC) ansatz
The paper Iterative Qubit Coupled Cluster approach with efficient screening of generators describes a new screening procedure for generators of the QCC ansatz.
How does one get from defining the ...
- 111
1
vote
0
answers
44
views
Can We Currently Import Quantum Datasets (Datasets Containing Quantum Data) Onto NISQ-era Quantum Computers?
I'm still investigating the TFQ whitepaper.
In one section of the paper, the authors say this with respect to Quantum Datasets
In general, [a quantum dataset] might come from a given black-box ...
- 195
1
vote
0
answers
50
views
Application Query [closed]
I had written earlier to propose an econometric modeling application that may lend itself to a quantum computing approach, and was asking how best to proceed.
The model would be centered around the ...
- 11