Questions tagged [quantum-computing]

A computation model which relies on quantum-mechanic phenomena, such as entanglement and superposition. This generalizes the probabilistic model of computation.

Filter by
Sorted by
Tagged with
2 votes
0 answers
28 views

Quantum Boolean SAT algorithm?

Is there a quantum SAT algorithm, a quantum analogue of the DPLL or CDCL algorithms? Note: I'm not looking for the quantum analogue of the Boolean satisfiability problem (though that would be ...
user avatar
  • 145
2 votes
1 answer
33 views

SAT and #SAT in Quantum

Let us look at the two questions that are NP-complete for a classical computer: Given an arbitrary Boolean expression, find an assignment of variables that evaluates the expression to $0$ (SAT). ...
user avatar
  • 297
0 votes
1 answer
41 views

What would be the conseuqences of BQP = NEXPTIME?

On wikipedia it says that $BQP ⊆ EXP$. However it is not known if $BQP \subset EXP$ Also I've seen that $PSPACE$ could contain $NEXP$ and does contain $BQP$. For this were assuming the incredibly ...
user avatar
1 vote
1 answer
32 views

Confusion about whats being processed in a quantum computer

Please correct me if im wrong but this is how I think quantum computers work. Say we have a q-bit. The q-bit is put through a quantum gate to put it into a superposition and manipulate its ...
user avatar
  • 35
1 vote
1 answer
44 views

What happens if we change $\mathcal{BQP}$ to allow quantum bits, but not quantum gates?

In the definition of the class $\mathcal{BQP}$ found in textbooks we (as the circuit builders) have access to an unlimited number of deterministic zero-initialized qubits and to a finite set of ...
user avatar
  • 428
0 votes
0 answers
26 views

Applying Hadamard Gate in Stern-Gerlach Experiment

My textbook describes a Stern-Gerlach experiment with the setup Z-X-Z. It says that the probability of measuring |0> with respect to |+> and |-> at the output of X is equivalent to applying a ...
user avatar
0 votes
0 answers
12 views

What are the chances of fusing a quantum computer and a parallel computer and what potential dangers/ benefits does it bring?

From my EPQ research I came to know that quantum computers require certain conditions to function optimally such as: low temperature so that electrons do not get disturbed etc. I've also read a book ...
user avatar
1 vote
0 answers
45 views

Is quantum computing a serious usable instrument for the IT industry?

Following this latest and very exciting research object I can't find till now a usable computer in that style. I would like to call actual quantum computing by the topic "researching of quantum ...
user avatar
1 vote
1 answer
110 views

What is the fastest classical "period-finding" algorithm that can replace the Quantum Fourier Transform in Shor's algorithm?

Shor's algorithm uses the Quantum Fourier Transform to find the period the function a^x mod N with "a" being a constant integer less than N and N being a ...
user avatar
0 votes
1 answer
30 views

Is it possible to use a quantum computer simulation to perform a cyber attack?

Is it possible to use a quantum computer and or a simulation to perform a cyber attack on classic computers? This is part of a research objective I'm trying to figure out.
user avatar
2 votes
1 answer
51 views

Why is CNOT the only non-trivial reversible gate for two input bits?

The Wikipedia page on the Toffoli gate mentions that CNOT is the only non-trivial reversible gate on two input bits. The CNOT gate computes the following function: $$ 00 \to 00 \\ 01 \to 01 \\ 10 \to ...
user avatar
1 vote
4 answers
57 views

Can quantum computers be modelled as a classical computer with access to an oracle?

Quantum computers can solve certain problems faster than classical computers e.g factoring numbers. and this is because quantum computers can do a fourier transform on $n$ qubits in $O(n^2)$ time as ...
user avatar
0 votes
1 answer
85 views

How will Big O be with quantum computers?

I don't even know if this is the right place to ask this this...but how will Big O be with quantum computers? More specifically, will the worst case always be constant? If yes, how will this change ...
user avatar
  • 1
1 vote
1 answer
47 views

What is the "formula" for "any cipher can be deciphered by a quantum computer"?

There are several quantum complexity classes in different ways analogous to NP: NQP, QMA, and, as I understand, others. P=NP BPP=NP in simple words means "any cipher can be deciphered by a ...
user avatar
  • 413
3 votes
1 answer
64 views

Is there a concept of probabilistic quantum computers?

Answering my question Yonatan N said a statement from which follows that there are computable functions of quantum time complexity strictly above polynomial. Accordingly a Quora answer Quantum ...
user avatar
  • 413
2 votes
3 answers
73 views

What is the computer science interpretation of a qubit?

I am a CS major trying to decipher quantum computing. I have done some elementary study on qubits and I always seem to get lost at the "infinitely many" states that the qubit can have. And I ...
user avatar
4 votes
1 answer
164 views

Why are complex numbers needed to define qubits?

I have started learning about quantum computing, and I have been told that you can forget about the physics and think of qubits as a natural generalization of the notion of bit. According to this view,...
user avatar
2 votes
1 answer
42 views

How do two H gates act on two entangled qubits?

In this circuit, if the two qubits are initialized at state 0, then after the oracle they are entangled and in the state: $$\frac{1}{2} (|00\rangle+|01\rangle+|10\rangle-|11\rangle)$$ My question is, ...
user avatar
  • 21
2 votes
0 answers
26 views

Special Properties for Oracles in HSP

Let $(G,+)$ be an abelian group, $X$ a finite set (of "colors"), and $f:G \to X$ a function such that there exists a subgroup $H<G$ for which $f$ separates cosets of $H$, i.e. $\forall a,...
user avatar
0 votes
1 answer
19 views

Relaxation possibilities of the lower bound worst case sorting algorithms without quantum computation

The sorting algorithms (merge-sort, quicksort...) are tought to have an absolutely hard lower bound which can not be outperformed by computation alone and this bound is $n*log_{2}(n)$, The reason for ...
user avatar
  • 141
1 vote
0 answers
36 views

BPP and BQP: Optimization Versions?

For optimization problems, I found complexity classes analog to some classes for decision problems, e.g. PO and NPO, mirroring P and NP for decision problems in the sense that optimization problems in ...
user avatar
2 votes
0 answers
29 views

Generalizing Quantum Computation

When you first learn more about computation you can imagine it in terms of boolean circuits. That is you get a boolean vector $v \in \lbrace 0,1\rbrace ^n$ which you can then apply a circuit $C$ to ...
user avatar
5 votes
1 answer
452 views

Can quantum computing help solve NP-Complete problems?

i was just wondering if quantum computing has done any good so far in solving NP complete problems. I am aware that quantum computing does solve some NP problems which are classically hard in ...
user avatar
0 votes
3 answers
685 views

What are analog and digital in computer science?

I once thought that any analog computer is any computer which "doesn't need electrical current to work". I once thought that any digital computer is any computer which "does indeed need ...
user avatar
  • 3
2 votes
1 answer
98 views

Is QMA known to contain Co-NP?

Is QMA known to contain Co-NP? If not, would Co-NP being contained in QMA have any implications for other complexity classes. (e.g. Causing the polynomial heirachy to collapse.)
user avatar
5 votes
1 answer
90 views

Factoring algorithms after number field sieves

It seems that the General Number Field Sieve (GNFS) became number one and then RSA stopped its factoring challenges and there have been no advances in factoring algorithms besides quantum computers. ...
user avatar
1 vote
0 answers
28 views

What is the simplest quantum algorithm to visualize a quantum computation?

I'm interested to visualize how a simple quantum computation can be done, step by step. Can you help me? I need any simple example of how qubits can be used to make a computation.
user avatar
4 votes
0 answers
318 views

Data structures for quantum computers

In classical computers we have List,Queue,Tree & etc data structures, since classical computers using 1's & 0's on those data structures. Then what happens when it comes to quantum computers, ...
user avatar
  • 141
3 votes
1 answer
87 views

Is there a complexity class QPP?

The complexity class PP is not considered tractable, because the probability of success can get arbitrarily close to 50% from above as the problem instances get larger, so that (e.g. if this approach ...
user avatar
  • 934
1 vote
0 answers
19 views

Why are MM-1QFA strictly more powerful than MO-1QFA?

While dealing with quantum finite automata (QFA), I repeatedly come across the statement that measure-many QFA (MM-1QFA, KW97) are strictly more powerful than measure-once QFA (MO-1QFA, MC97); both ...
user avatar
1 vote
2 answers
111 views

Can neural network process randomness?

So the question is : Is it theoretically possible to feed a neural network with some random values to expect an output since randomness is a lack of knowledge in most case. For this question, I've ...
user avatar
2 votes
1 answer
103 views

Can quantum computers really compute a vast number of possible solutions simultaneously?

This link says They are not constrained to stepwise calculations but, rather, can compute a vast number of possible solutions simultaneously—and at a speed that is far beyond anything we can ...
user avatar
  • 155
1 vote
1 answer
119 views

Understanding the state vector in Quantum Computing

I have just started to learn QC. It is said that The quantum state of $N$ qubits can be expressed as a vector in a space of dimension $2^N$ If there is $1$ qubit then we have two possible state ...
user avatar
  • 155
2 votes
1 answer
54 views

Understanding DIQKD protocol, a few questions

I'm refering to this paper here "Fully Device-Independent Quantum Key Distribution" (Umesh Vazirani and Thomas Vidick) and unfortunately there are many things I don't understand. 1) Page 3: by the ...
user avatar
  • 29
0 votes
0 answers
20 views

NDFA has maximum states as 2^n the same for qubits in quantum computation.How they can be distinguished in means of computation? [duplicate]

I am a Computer Engineer. I studied basics of Quantum Computation. In dealing with multiple states, I feel NDFA does similar to Quantum Computation but we preferred to convert NDFA to DFA and solved ...
user avatar
0 votes
1 answer
89 views

Does quantum computing convert any O(2^n) algorithm into a polynomial running time and how?

For example, if it is a $ O(2^n) $ algorithm that loops through 0 to $ 2^n - 1 $ and check whether the number of 1 bits is divisible by 3, 5, 7, 9, 11, does quantum computing reduce it to non-...
user avatar
2 votes
0 answers
57 views

What does it mean this relation: $BQP^{BQP} = BQP$

I am reading this paper by Fortnow, titled: One Complexity Theorist's View of Quantum Computing. In section 4, he states the following: Bernstein and Vazirani [BV97] show that BQP can simulate any ...
user avatar
  • 707
4 votes
1 answer
179 views

Can current quantum computers decide languages that Turing Machines cannot?

I am currently learning Computing Theory at university, and we were on the topic of Turing-Decidability, Recognizability, etc. Showing that a problem is undecidable with Turing machines due to ...
user avatar
  • 519
52 votes
3 answers
14k views

Why did Google not use an NP problem for their quantum supremacy experiment?

Reading discussions of the recent quantum supremacy experiment by Google I noticed that a lot of time and effort (in the experiment itself, but also in the excellent blog posts by Scott Aaronson and ...
user avatar
  • 673
14 votes
2 answers
1k views

Quantum Supremacy Task

I’m trying to understand the task performed by Google’s Sycamore that recently achieved alleged Quantum Supremacy. I’ve read the paper in Nature but the actual task that would have taken 10,000 years ...
user avatar
1 vote
2 answers
36 views

How do I search for Verification of Quantum Computing

So, in quantum computing, each qbit has a 50/50 chance of being in either the state of 1 or 0 when you measure it. Simple enough. But I've heard reports a while ago about some company having ...
user avatar
3 votes
1 answer
57 views

Does there exist any unrelativized separation between a quantum complexity class and a classical one?

I'm familiar with results of relativized separation for BPP-BQP, BQP-PH and NPC-BQP. I'm also aware that while e.g. Factoring is not believed to be in BPP, it hasn't been proven and so we're not quite ...
user avatar
2 votes
1 answer
98 views

BosonSampling: $\# P \subseteq FBPP^{{NP}^{\mathcal{O}}}$ implies $P^{\#P}\subseteq BPP^{{NP}^{\mathcal{O}}}$

I am a complexity beginner, actually a quantum physicist. In their famous BosonSampling paper, Aaronson and Arkhipov show amongst other things a polynomial time machine solving the problem of ...
user avatar
  • 161
1 vote
0 answers
45 views

Which is harder, an NP-complete problem or the Raz-Tal oracle problem?

This is a (hopefully) sharper version of a question that I asked previously. Which of these algorithms is believed to have a longer asymptotic runtime? The optimal algorithm guaranteed to solve some ...
user avatar
  • 934
5 votes
0 answers
113 views

The relationship between matrix inversion, the HHL algorithm, and the unlikely scenario that $BQP = PSPACE$

I am studying the quantum computing algorithm presented in the paper Quantum algorithm for linear systems of equations}. Without going through all the details, the HHL algorithm is able to apply an ...
user avatar
1 vote
0 answers
124 views

What is the complexity class of exponential parallelism?

Consider the class of problems that can be computed when you have access to exponentially many processors working in parallel. How does one capture that in a proper formalism? Is there some ...
user avatar
3 votes
1 answer
231 views

Basic complexity theory (in Oracle Separation of BQP and PH)

I have some basic questions about complexity theory that came up when I tried to understand the result by Raz and Tal that BQP$^O\nsubseteq$ PH$^O$. Aaronsons paper was helpful, but I still have some ...
user avatar
  • 155
1 vote
0 answers
38 views

Questions about Seth Lloyd's Programming the Universe?

I have been interested in Seth Lloyd's cosmological model (which proposes that the universe is a computer: https://en.wikipedia.org/wiki/Programming_the_Universe, https://arxiv.org/abs/quant-ph/...
user avatar
  • 11
0 votes
2 answers
84 views

Uncomputing measurement gate?

So one of Aaronson's lecture note (https://www.scottaaronson.com/democritus/lec10.html) pointed out that, if we'd like to simulate a BQP-oracle, technically speaking, the oracle of address-target form....
user avatar
3 votes
1 answer
61 views

Estimation of the number of solutions by Counting

This is a question from a quantum computation textbook. Consider a classical algorithm for counting the number of solutions to a problem. The algorithm samples uniformly and independently $k$ times ...
user avatar
  • 141

1
2 3 4 5