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6 views

Amplitude estimation over subspace of problem

I've been searching about quantum amplitude estimation techniques and read that it is customary to use an extra qubit to separate good and bad states using algorithm $A$ as $$ A|{0} \rangle^{\otimes^{...
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0answers
10 views

How to construct Hamiltonian for combinatorial optimization problems and then convert into Pauli basis?

Suppose I have a portfolio optimization problem where I have to minimize, $$qx^T\sum x - \mu^Tx$$ where q is the maximum risk and x is {0,1}^n and $\mu$ are the expected returns. Now I have to convert ...
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0answers
20 views

How to correct a phase error of the form $e^{ix}$

Is there a method to correct an error of the form of $e^{ix}$, acted on a two qubit state without knowing the nature (the value of x) of the error? Also, can I rephrase the above question to: Is there ...
0
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1answer
23 views

What is the convention of indices for the one and two-body integrals in qiskit

I was able to calculate the one and two-body integrals for the H2 with the following code ...
2
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0answers
19 views

What is the best way to use loop statements on a quantum computer?

I am interested in solving a time dependent linear partial differential equation of the form $Ax=b$ which, in classical computing, would amount to looping over solutions of $Ax=b$ where $b$ is updated ...
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2answers
38 views

Custom Gate/Instruction with classical bits in Qiskit

In Qiskit, I need to define a custom gate or instruction that, once decomposed, turns into a series of basis gates, including measurements and classically controlled gates (this is the part that I can'...
0
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1answer
29 views

How can I use the quantum volume to design the scale of my experiment?

I am designing an experiment which involves solving a linear system of equations of the form Ax=b. To do this, I am using the HHL algorithm on the IBMQ system. My ...
4
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2answers
33 views

Bell state preparation

I was watching some lectures on qubits. They were talking about how to generate a Bell state. They described it as follows: Prepare state 00: $$\left |0 \right> \otimes \left |0 \right>$$ Apply ...
1
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2answers
61 views

What is the matrix representation of the Hadamard gate in the computational basis?

I read about Hadamard gate H and found it's matrix representation as follows: $$H_1=\frac{1}{\sqrt 2}\begin{pmatrix}1 & 1 \\1 & -1\end{pmatrix}$$ I wanted to know what will be the matrix ...
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1answer
35 views

Quadratic optimization in Qiskit: Error when QuadraticProgram with quadratic constraint converted to QUBO

I prepared a quadratic optimization task with binary and integer variables and linear and quadratic constraints. I fed it into QuadraticProgram in Qiskit. After ...
3
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0answers
15 views

Reducing the depth of quantum circuits with ancilla qubits

This question is two-fold and considers general $n$-qubit operations on a quantum computer. First, can a general $n$-qubit operation be implemented on a quantum computer without the use of ancilla ...
2
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1answer
32 views

CNOT expressed with CZ and H gates by taking into account HZH =X

From this link: Where equation 1 is: I can probably brute-force this by explicitly calculating this quantum circuit's effective 4x4 matrix and seeing that its equivalent to this teleportation ...
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1answer
18 views

Implementing Partial Trace in IBMs quantum computer

I am trying to implement the partial trace operation on IBMs quantum computer. I am simulating the depolarising channel with the following code ...
0
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1answer
12 views

Implementing Cirq Coding Gates

Can someone please help me making these gates on CIRQ programming: Decrement Gate (-1) Splitter Gate (If possible) I was having trouble implementing these and was not sure if it's possible either. ...
1
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1answer
44 views

Hadamard gate for three qubits; inconsistency between IBM and Matlab

I am trying to build a large and quite complex three qubit quantum circuit on IBMs quantum computer. I have a specific unitary which I am trying to implement and I am building a circuit following the ...
2
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1answer
41 views

My IBMQ job hangs forever?

I am running a very simple script just to learn how to use IBMQ, but my job will hang indefinitely and I am forced to terminate it. ...
0
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1answer
22 views

Where does errors occur during error syndrome and recovery?

I'm studying quantum error correction on Nielsen's Quantum Computation and Quantum Information, but I don't understand how it identifies the number of places where an error may occur, it uses ...
2
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1answer
49 views

How can I convert the unitary matrix $e^\frac{i\pi}{2}$ into a quantum circuit in Qiskit?

How can I put the unitary matrix $$e^\frac{i\pi}{2}I$$ to the quantum circuit? I don't know if it is belong to $$U3(\theta, \phi, \lambda), U2(\phi, \lambda), U1(\lambda)$$ Thanks a lot.
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1answer
37 views

How to get state vector from QasmSimulator in Qiskit

I'm currently able to get state vector in Qiskit using state_vector backend using something like : ...
2
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1answer
39 views

Why running time of qasm simulator is significantly smaller in comparison with quantum machines?

I ran a 3-qubit measurement circuit on QASM simulator as well as on IBM Q Melbourne, Santiago and Vigo machines. The running time on the simulator is in few milliseconds (400-800) while in the case of ...
3
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0answers
29 views

Is there a measurable of entanglement for a macroscopic system?

After having a discussion with a quantum computing colleague, a question came up: is there any meaningful measure of entanglement in a macroscopic (i.e. many body) system where you don't have the ...
3
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0answers
53 views

What is the thought process for circuit making after seeing input and output of a matrix?

Here is an exercise (4.27) from Nielsen and Chuang and I found the answer (given in the figure below) online without any explanation. The question was to construct a circuit by seeing a matrix (given ...
1
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1answer
27 views

What is meaning of 'up to a global phase'? [duplicate]

What is the importance of global phase? How it affect a unit vector if we see it on a Bloch sphere? What is the meaning of 'up to global phase' in exercise 4.3 of Nielsen and Chuang?
1
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1answer
41 views

Counting Achievable Operations

I'm struggling to find an analytic way to solve this problem. There are $4! = 24$ possible classical operations on the four 2-Cbit basis states. How many of these are achievable via the classical ...
1
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2answers
30 views

What is the significance of transpiling time, validating time, in queue time and running time?

What is the significance of different transpiling time, validating time, in queue time, running time for the same circuit run on different quantum systems for same no. of shots in IBM Q experience? ...
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0answers
45 views

Please explain this definition in an article about quantum error correction

I'm reading this article which is explaining about quantum error correction and fault-tolerance. I'm wonder what "Definition 1" means. Especially, "There is C is an ((n, K)) (binary) ...
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0answers
42 views

Give an explicit derivation of the formula for the two-qubit absolute separability Hilbert-Schmidt probability $\approx 0.00365826$

The two-qubit eigenvalue ($\lambda_i$ >= 0, $i=1,\ldots,4$, $\lambda_4=1-\lambda_1-\lambda_2-\lambda_3$) condition of Verstraete, Audenaert, de Bie and de Moor AbsoluteSeparability (p. 6) for ...
2
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1answer
37 views

Is it required to input full matrix when using Qiskit HHL algorithm for sparse matrices?

I am working with a very sparse matrix and it seems inefficient to load the full matrix as input into the Qiskit HHL algorithm. Is it possible to input only the non-zero elements, instead ? I am ...
1
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1answer
38 views

Quantum Circuit Optimization with Machine Learning

I read some paper about Quantum Circuit Optimization but I am on a low level. And have some experience in ML. But what I don't understand is it possible that ML can help to optimize Quantum Circuits ...
1
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0answers
33 views

Deformation of the Bloch sphere and contraction of its planes under the action of channels

On pg 376-377 of N&C, it gives 3 different diagrams showing how the various axis of the Bloch sphere will be contracted under the action of the channels, limiting the possible states after it's ...
3
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1answer
98 views

How to implement linear combination of two unitary gates in a quantum circuit?

I wanted to implement a non-unitary operation. I came to know that I can do it as a linear combination of unitaries from this paper (published version). Let us say I want to implement an operation ...
1
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1answer
46 views

Obtaining hermitian matrix using Knill and Laflamme condition?

Let $E$ be the set of all correctable errors and $E_a, E_b \in E$. Let $\lbrace \vert c_1\rangle, \vert c_2\rangle, \ldots \vert c_k\rangle\rbrace$ be the basis of codewords in the codespace. It is ...
0
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1answer
54 views

What would be measured if you measure two entangled qubits at exactly the same time?

What would be measured if you measure two entangled qubits at exactly the same time?
2
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1answer
24 views

Splitting a quantum task between multiple devices

I've been wondering, are there any known tasks/algorithms that can be performed on 1 quantum device, but also be somehow modified and split between several smaller devices? The thought behind the idea,...
-1
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1answer
85 views

Implementing a circuit that returns $|01\rangle$ and $|10\rangle$ with equal probability

Using Python how can I implement a quantum circuit that returns $|01\rangle$ or $|10\rangle$ using only $CX$, $RX$ and $RY$ gates, starting with random parametric gates as parameters and optimizing it ...
1
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1answer
53 views

Question on output of SWAP test

Let's say I have two arbitrary quantum states $|\psi\rangle$ and $|\phi\rangle$. I apply the SWAP test circuit (something like what is given here), and measure the first qubit to get either $0$ or $1$....
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0answers
82 views

Can one use a quantum circuit as a pathfinding algorithm?

I've been learning about quantum computing, and I noticed that another way to describe the state vector is as a path in a binary tree where each level of tree represents another qubit, each node ...
-2
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0answers
33 views

Secret string in least significant bit with Simon algorithm

The function $f:\{0,1\}^2\to\{0,1\}$ , $f(x_1x_0)=x_0$ returns the least significant bit of its argument. Solve the Simon's problem for this function and write down the number "a" (secret ...
-1
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3answers
85 views

Google Colab - ImportError: The class MatplotlibDrawer needs pylatexenc

When I run the following command qc.draw(output='mpl') for my circuit qc, I get this error: ...
-1
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1answer
49 views

Least significant bit with Simon algorithm

would you kindly help me solve this problem: The function $f:\{0,1\}^2\to\{0,1\}$ , $f(x_1x_0)=x_0$ returns the least significant bit of its argument. What is the $U_f$ operator for this function?
0
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1answer
45 views

How to code a projector operator in qiskit?

I'm new to qiskit and I want to know how do I define a projector operator in qiskit? Specifically, I have prepared a 3 qubit system, and after applying a whole lot of gates and measuring it in a state ...
2
votes
1answer
54 views

Test equivalence of circuits exactly on qiskit

I have two circuits that I believe are equivalent. How can one check this on qiskit? Currently, I am executing both circuits and verifying that the counts are close (which they are) but I would like ...
1
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1answer
29 views

Is there a way to generate random circuits in qiskit with only certain allowed gates?

It seems like I can use https://qiskit.org/documentation/stubs/qiskit.circuit.random.random_circuit.html but I would like to control the gates that are allowed. What is an efficient way to make random ...
3
votes
2answers
47 views

Can Alice and Bob distinguish entangled state coefficients?

Suppose Alice and Bob share the quantum state $\frac{1}{\sqrt 2}(|x\rangle + (-1)^b |y\rangle)$ for some $x\neq y \in \{0,1\}^2$ and $b \in \{0,1\}$. They both do not know $x,y$, and use some ...
1
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1answer
25 views

Is entanglement nonincreasing on average by local operations for all possible ensemble decompositions?

We know for a pure state conversion $|\psi \rangle \rightarrow_\textrm{LOCC} |\phi \rangle$ via local operation and classical communication (LOCC), an entanglement monotone should not increase, that ...
-1
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0answers
36 views

Why are there 2 different versions of qiskit installed in anaconda?

When running pip show qiskit-ibmq-provider in the Anaconda Prompt I get the following: ...
1
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1answer
26 views

What is the significance of varying the number of shots while running a circuit in a quantum machine and qasm simulator?

what is the significance of varying the number of shots while running a circuit in a quantum machine and qasm simulator? Does more number of shots give better/accurate result? I am running a simple 2 ...
1
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0answers
27 views

Deriving Expression For QAOA Optimal Trial State Parameters

I am going through the QAOA section in the Qiskit Textbook - QAOA and am stuck in one of the steps. In section 5.2, the method for getting the Optimal Trial State Parameters are discussed. I do not ...
1
vote
0answers
39 views

What causes the random variations in the probabilities with respect to the theoretical values, in IBM and QASM simulators?

When I measure 2 and 3 qubits after putting H gate on all of them, there is a variation in probabilities of results in comparison with theoretical values (25% and 12.5%, respectively). This occurs on ...
0
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1answer
21 views

Is the combine_results method deprecated in qiskit v0.20.0

According to the ManagedResults Documentation the class has a combine_results method, however when attempting to use it as follows: ...

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