Questions tagged [quantum-gate]

For questions regarding usage, performance, implementation, application or theory related to quantum gates.

Filter by
Sorted by
Tagged with
1 vote
1 answer
23 views

How does an $\sqrt{X}$ error propagates through an $T$ gate?

I wonder whether there is a compact way of describing a noise $\sqrt{X}$ propagating through a $T$ gate. Possibly in terms of Pauli and/or Clifford operators.
user avatar
1 vote
2 answers
44 views

Multi qubit states and the CNOT gate

I'm stuck on this passage from a book: Suppose we try to copy a qubit in the unknown state $|ψ\rangle = a|0\rangle + b|1\rangle$ in the same manner by using a $\text{CNOT}$ gate. The input state of ...
user avatar
1 vote
1 answer
45 views

Can you construct a 3-qubit XOR state?

I'm wondering if it is possible to build a 3-qubit quantum circuit that creates the following pure state: $$\frac{1}{2}\left(|000\rangle+|011\rangle+|101\rangle+|110\rangle\right)=\frac{1}{2}\left[1,0,...
user avatar
  • 77
2 votes
1 answer
37 views

How does the Pauli Y gate act in the $|+\rangle, |-\rangle$ basis?

The X gate in the $|+\rangle$, $|-\rangle$ basis becomes the Z gate and vice versa. What is the Pauli Y gate as a matrix transformation in the $|+\rangle$, $|-\rangle$ basis?
user avatar
0 votes
1 answer
79 views

Is there the number of CNOT restriction?

I know that there is connectivity restriction when implementing physical CNOT gate. But, I wonder if there is a limit to the number of physical CNOT gates that can be performed at the same time. For ...
user avatar
1 vote
1 answer
32 views

I have question about cost of 'modular multiplication unitary' in Shor's algorithm

Here modular multiplication unitary means $U_a : |s\rangle \to|as\mod N\rangle$. My main question is, can the modular multiplication unitary $U_a$ can be constructed in time polynomial in the number ...
user avatar
1 vote
0 answers
33 views

Slight issue with QFTing two qubits

Let's consider two qubits and the corresponding computational basis $\{|0\rangle\, |1\rangle, |2\rangle, |3\rangle\}$. In binary form, any of these vectors can also be written as a product $|x_1\...
user avatar
1 vote
0 answers
35 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 ...
user avatar
3 votes
0 answers
78 views

What is the correct name of this quantum gate? Possibly state control gate

Let $\vec v \in \mathbb{C}^2 $ be the following quantum state: $$ \vec v = \frac{1}{\sqrt{2}}\begin{bmatrix} v_{1} \\ v_{2} \\ \end{bmatrix},\space \lvert v_1 \rvert = 1,...
user avatar
1 vote
1 answer
53 views

math behind rotation gate

$R_Z(\theta) = e^{-i\frac{\theta}{2}Z}$ and $R_{ZX}(\theta) = e^{-i\frac{\theta}{2}XZ}$ My question is, why is the rotation gate defined in an exponential format? Where does the $\frac{1}{2}$ come ...
user avatar
  • 1,223
1 vote
1 answer
27 views

Gate times for photonic quantum computers

I am trying to understand the landscape of one- and two-qubit gate times for various quantum computing architectures. It is not so hard to find gate times for various gates such as Hadamard, CNOT and ...
user avatar
  • 409
5 votes
1 answer
723 views

Is 60% accuracy high when calculating 1+1 on a quantum computer?

A financial firm has criticized the quantum computer of a company called IonQ. Part of the content is that IonQ's quantum computer is only 60% accurate for 1+1 calculations, and only 50% for 2+3 ...
user avatar
  • 51
1 vote
1 answer
53 views

Counting the number of CCX and CX gates in controlled modular addition

If we do a controlled modular addition of an adder with 2n ccx and 4n cx gates for example the CDKMRippleCarryAdder, what will be the resultant count of ccx and cx ...
user avatar
  • 13
2 votes
0 answers
44 views

How do I generate gates for qudits with $d=4$?

So I was working on a project with qudits (specifically d = 4) and came across a problem. How do I generate gates for these? I can construct Hadamard and X gates for these, but how does one approach ...
user avatar
  • 33
2 votes
1 answer
37 views

What is the average amount of gates needed to implement a random Clifford gate?

Given a Clifford gate acting on $n$ qubits is implemented using its generators, what is the average number of gates needed to implement a random Clifford gate as a function of $n$?
user avatar
0 votes
2 answers
51 views

Create a 2-qubit quantum circuit with given state probabilities

Let's say we are given two probability values $p_1 > 0$ and $p_2 > 0$, with $p_1+p_2 \leq 1$ but not necessarily equals to $1$. We are asked to create a 2-qubit quantum circuit with state $|01\...
user avatar
0 votes
2 answers
70 views

Rxx gate as a set of rotations

I'm trying to represent Rxx gate as a set of physical rotations of two qubits in 3D space (or as rotations of Bloch Spheres that is the same). In some simple cases it works well: If q0 is in the ...
user avatar
1 vote
1 answer
45 views

Sending messages via CNOT gates

Consider a situation in which each of Alice, Bob and Charlie holds a qubit, where the three qubits are acted on by a 3-qubit gate $U$. Assume that the gate $U$ can be implemented by first performing a ...
user avatar
0 votes
1 answer
15 views

Qiskit library.gaussian() does not accept parametric expression

I'm trying to build a gaussian pulse in qiskit where I keep the amplitude as a parameter but for the followig code ...
user avatar
  • 1
0 votes
1 answer
44 views

Quantum gates defined in SpinQ desktop computers

There is manufacturer of desktop quantum computers: https://www.spinquanta.com/products. There are few models on the market: Gemini Gemini-Mini Triangulum Lyra Does anyone know where to find quantum ...
user avatar
  • 302
1 vote
2 answers
313 views

Can anybody explain the following circuit?

I think I understand what it does. But i can't agree with output for sertain inputs. For example: if a=1 and b=1 then how the output on 4 line could be xor(a, b). Because as far as I know xor(1,1)=0 ...
user avatar
  • 21
0 votes
1 answer
28 views

Generating a random 32-byte hex integer using Qiskit

Hello I posted here yesterday about generating random 16 digits using Qiskit, and a gentle guy helped me but how about a string? How can I generate random 256 bit key in hex format in a superposition ...
user avatar
2 votes
1 answer
38 views

Question about mock backends!

I recently learned about the mock backends or the fake backends provided by Qiskit and I was wondering, do they behave the same way IBMQ systems backends like (ibmq_brooklyn)? also, can I depend on ...
user avatar
0 votes
1 answer
44 views

Generating a random 16-digits in a superposition state using Qiskit

Im trying to create a script using Qiskit for a days but somehow i couldn't seem to get it done!! Im new to QuantumComputing, so pardon me if i don't explain something properly. I need to create a ...
user avatar
2 votes
1 answer
39 views

Quantum gates for more than two basis states

Lets say I have a time dependent hamiltonian of the form $$H(t) = H_0 + f(t) H_{drive}$$ (where $H_0$ may represent the hamiltonian for a superconducting qubit) and I want to find the optimal pulse $f(...
user avatar
  • 21
1 vote
1 answer
547 views

How does a quantum computer find the correct password faster than classical computers using brute-force?

I didn't get this part right! For example, we have an online box with a 16-digit password, and we don't know what the password is! How can a quantum computer find the correct password faster than ...
user avatar
1 vote
1 answer
57 views

Grover's Search Number of iterations for M > 1

In Grover's Search algorithm, how to determine the number of iterations for any $M$ such that $1 < M < N/2$? The calculations given in the Nielsen and Chuang book say that $R \leq \frac{\pi}{4} ...
user avatar
4 votes
1 answer
50 views

There exists an efficient gate that swaps values of different superposition kets?

Is there an efficient gate that swaps values of different superposition kets? Let $ \alpha_i, \beta_i $ be string in $ \{0,1\}^n$, I'm wondering if there are a known results about the existence of ...
user avatar
2 votes
2 answers
60 views

IBM Quantum Experiment CNOT

I have a beginner question regarding CNOT-Gates on IBM Quantum. Assuming the following simple circuit: ...
user avatar
1 vote
1 answer
41 views

What is the time overhead for fault-tolerant gate teleportation?

The gate teleportation protocol (https://arxiv.org/abs/quant-ph/9908010) has a step where it utilizes cat state measurement of transversal operators. Since cat states can not detect phase errors it is ...
user avatar
  • 236
4 votes
2 answers
145 views

Is there a way to convert a superposition $\sum_i a_i |x_i\rangle$ into $\sum_i |a_i,x_i\rangle$?

I am wondering if there is a way to convert a superposition $$\left|\phi\right>=\sum_{i}a_i\left|x_i\right>$$ into $$\left|\phi'\right>=\frac{1}{|{\rm norm}|}\sum_{i}\left|a_i,x_i\right>,$$...
user avatar
2 votes
0 answers
17 views

What is a realistic model for simulating physical tampering of a channel? (ex: nearby vibrations)

Somewhat related to this question. Imagine a fully functioning quantum network, where qubits are transported via fiber optic cable. If vibrations were to physically tamper with a channel in such a ...
user avatar
2 votes
2 answers
86 views

Why does gate teleportation allow to implement nonlocal operations via local ones?

In (Gottesman and Chuang 1999), when discussing quantum gate teleportation, they mention how it can be used to implement nonlocal gates such as a CNOT, by only using (classically controlled) local ...
user avatar
  • 18.1k
2 votes
1 answer
42 views

How does quantum gate teleportation differ from state teleportation?

As described e.g. in this post, quantum gate teleportation can be framed as a variation of quantum state teleportation where a gate is applied beforehand on the receiver, and this results in the final ...
user avatar
  • 18.1k
1 vote
1 answer
40 views

Manually calculating quantum circuit with custom gate

I am trying to calculate the state of this Quirk circuit by hand: where U is a custom gate with 2x2 matrix: From what I've read, I should be able to calculate the resultant amplitudes as: (U⊗I⊗I).(...
user avatar
5 votes
0 answers
60 views

Given a non-Clifford quantum circuit $U$, is it possible to construct a commuting Clifford circuit $C$?

Given a non-Clifford circuit $U$, say $U = \prod_{i=1}^k e^{i \theta_i P_i} $ for $P_i \in \{ I,X,Y,Z\}^{\otimes n} $ and $\theta_i \in \mathbb{R}$. Is it possible to construct a non-trivial Clifford ...
user avatar
  • 12.3k
4 votes
0 answers
87 views

Is the Eastin-Knill Theorem incorrect?

I am reading through this paper (the Eastin-Knill Theorem) and there is a step in the proof of the main theorem that I do not understand. Let $Q$ be a composite quantum system supporting a quantum ...
user avatar
  • 287
0 votes
1 answer
26 views

What’s the proper gate use for the following code? (Python)

I am trying to find a proper way to write a code that will give me the resulting quantum state $i|10\rangle$ using qiskit in Python (using Jupiter notebook). I think I have figured out that the ...
user avatar
  • 103
1 vote
1 answer
92 views

State Initialization of quantum circuit

I am trying to understand how to initialize a quantum circuit with classical input. By browsing on the internet, I came to the conclusion that there are some fixed circuits which can be used to ...
user avatar
1 vote
1 answer
93 views

Is there a way to rotate an unknown state towards another known state?

I would like to rotate my $|\Psi\rangle$ state towards $|1\rangle$: $$ |\Psi\rangle= a|0\rangle + b|1\rangle \ \rightarrow \ |\Psi'\rangle= a'|0\rangle + b'|1\rangle$$ with $|a'| < |a|$, $|b'| > ...
user avatar
4 votes
2 answers
77 views

Standard name for CZ gate conjugated by Hadamards?

Is there a standard name for a $CZ$ gate conjugated by $H \otimes H$ gates? See below for circuit
user avatar
2 votes
1 answer
35 views

Direction of rotation operators

The rotation operators for a single qubit are defined as $R_{v}(\theta) = e^{-i \theta X/2}$, with $v \in \{ X,Y,Z\}$. If we look at the direction of rotation of $R_v$ w.r.t. the positive eigenvalue, ...
user avatar
3 votes
2 answers
59 views

What justifies using tensor product of matrices for parallel gates when applying them to an entangled state?

In my university we defined tensor product of two matrices $A$, $B$ as a matrix $A \otimes B$ such that for any vectors $\left| \phi \right>$, $\left| \psi \right>$ the following is satisfied: $$...
user avatar
  • 33
2 votes
1 answer
94 views

Does the CX gate always leave the first qubit unchanged and swap the amplitudes of the second one?

I'm a self-learner of quantum computing and is at the very beginning. I do have some math and coding background though. I'm trying to understand how working with entangled qubits helps performing ...
user avatar
  • 123
1 vote
2 answers
61 views

Is there relation between IonQ native gates and the rotation gates $R_x$, $R_y$, $R_z$? [closed]

I know $GZ = R_z$ and $XX = MS$ but what about $GPI$ and $GPI2$?
user avatar
2 votes
0 answers
21 views

How to extract solution from HHL statevector on qskit?

I want to extract the HHL solution from the StateVector. I am doing this on a $4\times4$ matrix. For a $2$ by $2$ the solution is available in the StateVector $8$, $9$. However for a $4$ by $4$ matrix ...
user avatar
2 votes
0 answers
76 views

Local Hermitian operators can be written as sums over local error operators?

In this paper, near the bottom of the left half of page 3, the authors claim that any local Hermitian operator (one which acts only on a single subsystem of a larger composite system) can be expressed ...
user avatar
  • 173
1 vote
1 answer
21 views

Quantum Gate - Negating qubit whose state is known to lie in the equatorial x-y plane

Given a qubit whose state is known to lie in the equatorial x–y plane in the Bloch sphere is it possible to find a quantum gate that will always negate this qubit? If so, exhibit such a gate. If not, ...
user avatar
  • 11
0 votes
0 answers
75 views

How can I solve problems with quantum computers ? (Methodology)

I am reading these days a book about programming quantum computing using the language Silq. I reached half the Silq book. The good thing about the Silq book is that it teaches the mathematics of ...
user avatar
1 vote
2 answers
80 views

Is there a way to map the Cu3 gate to represent a unitary matrix whose elements are complex in nature

I have this 2*2 unitary matrix one looks like U =[ -0.2840 - 0.5319i, -0.0000 - 0.7978i; -0.0000 - 0.7978i ,-0.2840 + 0.5319i] I want to represent this unitary matrix by a CU3 gate which looks like ...
user avatar

1
2 3 4 5
24