Questions tagged [circuit-construction]
For questions about the construction of complex circuits using elementary quantum gates.
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Method to mark only when certain conditions are satisfied in the superposition states of qubits
I am Newbie in Quantum Computing World.
While studying on my own, I was curious about one thing, so I asked this question.
My question is as follows:
When I configure the superposition states of ...
2
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1answer
49 views
Can Qiskit decompose circuits into non-IBMQ basis gate sets?
Let circ be a QuantumCircuit object. Running circ.decompose() returns a circuit that ...
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19 views
Circuit diagram that can produce the state $|\zeta_{ABE}$ in Eve’s laboratory
Consider the entanglement-based protocol that in each round Alice prepares a Bell state $(|\Phi_+\rangle= \frac{1}{\sqrt{2}}(|00\rangle+|11\rangle)=\frac{1}{\sqrt{2}}(|++\rangle+|--\rangle)$ and ...
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QAOA Circuit for MWIS
Hi thanks for taking a quick look!
I’ve got a question of how weights are implemented in the angles for gates in the QAOA.
I'm trying to solve the Maximum Weighted Independent Set Problem
This is the ...
2
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1answer
40 views
Is there any way to assign a colour for a single gate in Qiskit?
I'm drawing with Qiskit a big circuit with some predefined and custom gates. I want to colour some of them in non-default colours for a better reading of it. Is it possible to do it for predefined ...
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1answer
44 views
Expectation value of an arbitrary observable. My own definition and `cirq` limitations
In my previous question I was struggling with the definition of expectation value of an observable for a circuit. Here is what I have derived after some support (I simplify the definition to 2-qubit ...
3
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1answer
68 views
Multiplying quantum circuits in cirq using * and computing “expectation values”
I am reading cirq guide about Simulation and there is an example in "Expectation values" paragraph that I don't understand.
Everything boils down to the following snippet:
...
2
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1answer
71 views
Using principle of deferred measurement to replace gates conditional on classical bits (c_if)
I am trying to implement the Iterative Phase Estimation algorithm on one of Qiskit's labs. I can do it for a 'nice' phase, such as 1/4 :
But if I want to implement the algo generally (as a subroutine ...
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1answer
41 views
Single qubit gates (or CNOT) sequence to transform SWAP to Sqrt of SWAP
I'm trying to figure out how to transform the SWAP state gate into the square root of SWAP gate using only CNOTs or single qubit gates.
As you might guess, I'm new to this whole concept, but I'm ...
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2answers
110 views
Computing $e^x$ on a quantum computer
Does anyone know how to make a quantum circuit to compute exponentials where the exponent can be a fraction? To be more precise, I'm looking for a fixed point quantum arithmetic circuit that does the ...
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59 views
Exponentiating Pauli matrices using trapped ion native gates (single-qubit rotations + XX, YY, ZZ)
I'm wondering what are the known/good/standard ways of exponentiating Pauli terms (i.e. constructing circuits, which implement $\exp(i\alpha XIIZYI...)$) using gates supported by trapped ion quantum ...
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1answer
50 views
From mathematical notation to quantum circuit, in general
I am learning the basics of quantum computing using Qiskit and I encountered a problem when I tried to solve some of our course exercises. I feel like I am missing an invisible step, the step from ...
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1answer
44 views
Conditional Statements on a Quantum Computer
I've been struggling with this for a while now, and whilst I suspect the answer is unknown or very complicated, I thought I'd ask regardless.
Suppose I have some states $|\psi_i\rangle = \sum_{j=1}^n ...
2
votes
3answers
110 views
Find unitary such that $U:|i\rangle|0\rangle\rightarrow|i\rangle|A_i\rangle$
Let's assume I have two qubits of state $|A_0\rangle$ and $|A_1\rangle$ correspondingly stored in a quantum memory. How do I find a Unitary $U$ that acts on another register of 2-qubits such that
$$U:|...
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1answer
61 views
How to make a half adder for x number of qubits with min. cost?
How to make a half adder for N inputs and getting the output on another x+1 output. Where x ...
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43 views
3-qubit phase shift gate/circuit implementation without any Ancilla qubits
Hi, I need help me with figuring out the 3-qubit phase shift circuit without any ancillas similar to the 2-qubit circuit shown in below attached picture....... Please do let me know! Thanks in advance!...
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1answer
35 views
Implementing a SwapTest for samples with large numbers of features
I am trying to calculate the distance between sets of vectors. To do this I can create a SwapTest circuit (described here on page 34) and encode a feature vector with a U3 gate, then apply H and CSWAP ...
3
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1answer
107 views
What is the action of sandwiching an operator with two CNOT gates?
When a gate is sandwiched (or conjugated) by two CNOT gates, what effect does it have on the gate being sandwiched? For example, in the figure below, it is clear what effect the controlled $R_y(\theta)...
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1answer
38 views
Partial Cyclic Permuation with only Toffoli and CNOT gates?
I have been trying to solve this puzzle of constructing this transformation from CNOT and Toffoli gates as mentioned in NC page 193 (Ex 4.27)
Here is what I have done:
First observation is it has 8 ...
3
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1answer
64 views
How can I create an ADD gate for two quantum states? [duplicate]
I want to create an ADD gate like this:
in qiskit using elementary gates.
Can it be done?
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0answers
68 views
Is there a systematic way how to generate the Hamiltonian from a given circuit?
If I have a designed circuit to solve a particular problem. Is there a systematic way how to generate the Hamiltonian from it?
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1answer
57 views
Parametric circuit to prepare the most general single-qubit state [closed]
I am highly confused with this statement and spent a lot of time understanding it.
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1answer
58 views
How can I find a Clifford+T approximation of an arbitrary one qubit gate in Qiskit?
I know the Solovay-Kitaev algorithm can achieve this. Is there an implementation of this or any other algorithm for the same task in Qiskit? Or perhaps some other library that interfaces well with ...
3
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1answer
46 views
Circuit that measures PVM
How can I construct a circuit that measures PVM $\{|\psi\rangle\langle\psi|\},|\psi^\perp\rangle\langle\psi^\perp| \}$ where $|\psi\rangle=\cos\frac{\theta}{2}+e^{i\phi}\sin\frac{\theta}{2}|1\rangle$ ...
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2answers
110 views
Qiskit order of multiplication and tensor product
Section 2.3 of the Qiskit textbook shows us that
$$ CNOT|0+\rangle \ = \ \frac{1}{\sqrt2}(|00\rangle + |11\rangle)$$
which I was able to translate to a circuit as such:
...
4
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2answers
86 views
Preparing Bell state $(1/\sqrt{2}) (|01\rangle + |10\rangle)$ in Qiskit
I'm working through the Qiskit textbook right now, and wanted to complete part 1 of exercise 3.4, which asks me to use qiskit to produce the Bell state:
$$\frac{|01\rangle + |10\rangle}{\sqrt{2}}$$
...
3
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1answer
82 views
Efficient QFT-based QPEA complexity
The HHL algorithm lies on an implementation of the Quantum Phase Estimation algorithm. One popular implementation is based on the Quantum Fourier Transform which can be divided in three steps. Let $U$ ...
3
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1answer
126 views
How to construct a controlled-Hadamard gate using single qubit gates and controlled phase-shift?
How can I construct a controlled-Hadamard gate using single qubit gates and controlled phase-shift?
I am stuck in this and any help would be appreciated.
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27 views
How can I construct a Controlled-Hadamard gate using single qubit gates and Controlled phase-shift? [duplicate]
I am stuck in this and any help would be appreciated.
3
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1answer
60 views
Cirq: n-qubit GHZ state
I am trying to write $n$ party GHZ state but at the end of the day, it seems like bi partite state. I am missing a detail. Here is my code
...
3
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1answer
113 views
How does a rotation about the y-axis on a Bloch sphere affect the state of a qubit?
I am unsure how exactly it can be inferred that the following sequence of logic gates and rotation operators acting on a three-qubit state $\lvert abc\rangle$
$$ R_{y,c}\left(\frac{\pi}{4}\right)CNOT(...
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3answers
97 views
How to create the state $\vert 0 \rangle+i \vert 1 \rangle$ using elementary gates?
I am trying to write $|0\rangle+i|1\rangle$ in terms of elementary gates like H, CNOT, Pauli Y, using the IBM QE circuit composer.
I was thinking some kind of combination of H and Y since $Y|0\rangle=...
6
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1answer
218 views
Distinguishing collapsed and uncertain qubit in a quantum circuit
I have been through the Young's double slit experiment. It's a direct proof or instance of showing that a wave is collapsed via observation or measurement, and shows no interference patterns.
I want ...
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1answer
50 views
What is a complexity of producing arbitrary equally distributed superposition?
In the article An Optimized Quantum Maximum or Minimum Searching Algorithm and its Circuits I found statement (pg. 4):
Preparing an initial state takes $\log_2(N)$ steps.
In this case the initial ...
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1answer
59 views
How to deal with job submission error in IBM? [closed]
I keep on getting this error no matter how many circuits I run in the backend 'ibmq_athens'. It says 'Max retries exceeded with URL'. Can someone explain why I am getting this error message.
The main ...
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114 views
Is there an efficient circuit implementing the unitary $U|x\rangle|0\rangle=|x\rangle\Big(\sqrt{1 - x/2^n}\,|0\rangle+\sqrt{x/2^n}|1\rangle\Big)?$
Given an $n$-qubit register $|x\rangle$, does there exist an efficient circuit implementing unitary operation $U$ such that
$$U |x\rangle|0\rangle = |x\rangle\Big(\sqrt{1 - x/2^n}\, |0\rangle + \sqrt{...
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1answer
78 views
Are there any algorithms that take measurements in an intermediate step?
As a beginner in quantum computation, I noticed that all quantum algorithms take various gates followed by measuring the qubits in the last step. Is it always the case? Are there any algorithms that ...
3
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2answers
82 views
How do you represent one-quibit rotations in two registers as its own 4x4 unitary matrix?
Let's say you have a circuit that performs a Z-rotation in the first register, and a Y-rotation in second register. How can we express this "moment" in terms of a 4x4 matrix, i.e. a two-...
2
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1answer
68 views
Decomposition of 2-qubit Hamiltonian into standard gate set for QAOA
I try to decompose ansatz into gate set in order to create a circuit in qiskit for QAOA algorithm.
I don't understand how represent parametrized 2 qubit ansatz as circuit.
$ H{_B} = \sum_{j=1}^{n} {\...
6
votes
1answer
170 views
Trying to understand this measurement of a simple quantum circuit
It's a newbie question, I know. But I was just wondering if someone could help me understand why this simple circuit results with the measurement shown. I've just didn't get the last step. It's not ...
4
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1answer
132 views
How to effectively compute eigenvalue rotation in HHL
In the HHL algorithm, how do you efficiently do the $\lambda-$controlled rotation on the ancillary qubit ? It seems to me after reading around some answers that this can be done in two steps :
First, ...
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1answer
63 views
How to build a Hilbert space when do we already have concrete quantum logic gates available?
I read here that we use matrices to represent quantum logical gates.
But I don't like this 'point of view' because I want to build (or simulate logically with a real quantum processor, not through ...
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0answers
41 views
Quantum Search/Count on an unknown superposition state
Question:
Search a 'known' element in an 'unknown' quantum database
Alternatively, show this is fundamentally impossible (somehow related to the Holevo bound or P < NP?)
Related yet different:
...
2
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2answers
80 views
Conjugate transpose of a U-gate
I want to be able to create the circuit depicted below, but running the code below results in an empty circuit when viewing the job afterwards.
...
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1answer
78 views
Prepare state $|00\rangle+|1+\rangle$ using Clifford gates and the T-gate
I am looking for a quantum circuit which maps state $|00\rangle$ to $|\psi\rangle=\frac{1}{\sqrt{2}} |00\rangle+\frac{1}{\sqrt{2}}|1+\rangle$.
The circuit should only apply quantum gates from the ...
6
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3answers
99 views
Decomposing gates resembling exponentiated members of desired gateset
Suppose I have access to a pretty typical gate set, for example $\{\text{CNOT}, \text{SWAP}, \text{R}_{x}, \text{R}_{y}, \text{R}_{z}, \text{CR}_x, \text{CR}_y, \text{CR}_z\}$ where $\text{CR}$ is a ...
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1answer
41 views
Device Repitition Rate on Melbourne
I've been receiving "Circuit runtime is greater than the device repetition rate [8020]" errors when running a relatively simple circuit on ibmq_16_Melbourne, but have had no issues ...
4
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1answer
374 views
Is there a way to create a superposition of all the possible states?
If there're four qubits in my circuit, how can I arrange my gates so that the final output state is a superposition of all the possible states of 4 qubits? (there're 16 of them in total). I've tried ...
3
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1answer
45 views
How to change the sign of a phase: sending $\alpha|0\rangle+e^{i\alpha}\beta|1\rangle$ to $\alpha|0\rangle+e^{-i\alpha}\beta|1\rangle$?
Say I have a qubit in the state (ignoring normalization) $$|\phi\rangle = \alpha|0\rangle + e^{i\alpha}\beta|1\rangle.$$
How can I invert the sign of its phase, thus making it $$\alpha|0\rangle + e^{-...
