All Questions

0
votes
0answers
6 views

Does an Oracle use only the eigenstates of the quantum register?

The working of a quantum oracle is still not completely clear to me and I have a few questions: As I understand it, an oracle is a unitairy quantum gate and must somehow differentiate between the ...
1
vote
0answers
8 views

How to add states on the Bloch sphere from a master equation?

Can you please help me to find an answer to this question: I am using qutip for the study of quantum systems. suppose I have calculated the solution of the master equation using the ...
1
vote
0answers
10 views

How to represent $|+\rangle$ in Python?

I am using state vectors and operator matrices to test out my knowledge in a Python program. How would I represent the state $|+\rangle$ in Python? I want to then perform several operations in a ...
1
vote
0answers
8 views

Understanding CNOT gate for indirect measurement

I am trying to write a simple circuit to understand the process of finding the set of parameters such that the cost function of that circuit in question is minimized. For that I understand one has to ...
1
vote
0answers
16 views

Understanding the “Controlled Rotations” used in the HHL algorithm

In the HHL paper they make use of what they refer to as a controlled rotation in order to invert the eigenvalues of a Hermitian matrix $A$, which is what I am trying to understand. I understand the ...
1
vote
3answers
45 views

Controlled Z gate acting on 3 qubits in matrix form

For a controlled Z gate $CZ_{1,2,3}$ acting on 3 qubits, which of the following is correct? If it is the first one then what is the difference between that and a CZ gate acting on qubits 1 and 3? $$I ...
-4
votes
0answers
16 views

What if I say computing without a (computer), no device? or unit or machine [on hold]

Natural 100% adding up what computers were invented for. Ourselves a processor, autonomously. Thru neural supremacy. Individual person with the right timing and thought process in his brain whom will ...
3
votes
1answer
10 views

Bug in IBM backend?

I was trying to see what IBM would do under the hood with a CCNOT gate. Something appears to be erroneous with the run. The circuit above should produce state 11100 with 100% probability, as ...
3
votes
1answer
14 views

2 ways to do the three qubits bit-flip code

I'm trying to understand the three qubits bit-flip code. I use the book of Phillip Kaye An introduction to quantum computing. In this book he introduce the three qubits bit-flip code with this ...
2
votes
0answers
9 views

Geometric interpretation of 1-distillability

This is a sequel to Motivation for the definition of k-distillability Geometrical interpretation from the definition of 1-distillability The eigenstate $|\psi\rangle$ of the partially ...
4
votes
0answers
21 views

Motivation for the definition of k-distillability

Definition of k-distillability For a bipartite state $\rho$, $H=H_A\otimes H_B$ and for an integer $k\geq 1$, $\rho$ is $k$-distillable if there exists a (non-normalized) state $|\psi\rangle\in ...
3
votes
0answers
27 views

Bell State 11 not working for parity curve

I am currently writing a script to automate the creation of parity curves for a 2 qubit bell state and then calculate fidelity and proving entanglement from that (inspired by this paper). It was going ...
3
votes
0answers
16 views

How many two-qubit gates required for general N-qubit unitary?

Is there a known formula or a scaling behaviour for how many two-qubit gates are required to construct a general N-qubit unitary? I suppose there are several cases to consider: Exact representation ...
4
votes
1answer
40 views

Using the HHL algorithm to compute $A |b \rangle$ instead of $A^{-1} |b \rangle$

In the paper "Compiling basic linear algebra subroutines for quantum computers" here, they discuss (page 2 bottom right) using the HHL algorithm to multiply a vector by a matrix. However, after ...
5
votes
0answers
62 views

Calculating power of a quantum computer — RSA

As discussed in this question, the expected security of 1024-bit RSA is 80-bits: NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength ...
5
votes
1answer
31 views

$n$ qubit vs. a $d=2^n$ qudit states and measurements

The pure states of a qudit inhabit the $\mathbb{CP}(d-1)$ manifold. Is it true that the pure states of $n$ qubits live on the $\mathbb{CP}(2^n-1)$ manifold? If the answer to the first question is yes,...
4
votes
1answer
100 views

Understanding the classification of quantum states based on partial transposition: representations of the bipartite density matrix

I'm going through some slides on the PPT/NPT criteria along with Horodecki's paper, and I'm kind of stuck. Let's take this slide: Firstly, why can we write a bipartite density matrix as $\sum_{...
1
vote
1answer
35 views

Construction of Phase Shift Operation used in Quantum Search

In Chapter 6 of "Quantum Computation and Quantum Information" Textbook by Nielsen and Chuang, Box 6.1 gives a circuit example of Quantum Search Algorithm done on a two-bit sized search space. The ...
2
votes
1answer
41 views

IBM Slack links broken

Does anyone know where I can find working Slack invite links to any of IBM's Slack pages? The Slack links on this support page are all broken. Thank you.
1
vote
0answers
26 views

Superdense coding projects

I have recently been studying quantum computing specially the cryptographic aspects of it. The books I followed is Nielsen and Chuang, and a book named Quantum Computing Explained by David McMohan. ...
2
votes
2answers
438 views

How to compute the inverse of an operation in Q#?

I want to implement amplitude amplification using Q#. I have the operation $A$ that prepares my initial state and I need to compute $ A^{-1} $ to implement the algorithm. Is there an easy way to do ...
2
votes
0answers
19 views

How to prove the following bosonic entanglement expression?

Based on the article given by J. L. Ball, I. Fuentes-Schuller, and F. P. Schuller, Phys. Lett. A 359, 550 (2006) had used the following expression of von-Neumann entropy \begin{equation} S = - \...
5
votes
1answer
21 views

If the quantum Fourier transform efficient if only one control-phase is allowed in the gate set

I have seen Why can the Discrete Fourier Transform be implemented efficiently as a quantum circuit?. This is not a duplicate. I am familiar with the decomposition of the QFT from Nielsen&Chuang ...
1
vote
2answers
39 views

CX gate with Hadamard

Let's say we got a CX with a Hadamard gate on the control gate and any state at the target gate, will the target necessarily become a superposition of two states? Best.
3
votes
1answer
47 views

Implementing a complex circuit for a Szegedy quantum walk in qiskit

Problem definition I'm implementing a quantum circuit in qiskit for a Szegedy quantum walk, (reference, Fig 21.). It uses two registers of dimension $N$ ($N=3$) each one. The challenges I'm facing ...
2
votes
0answers
31 views

GHZ - measuring particles

I'm referring to an earlier question. It involves secret sharing based on the different measurement directions 3 people i.e Alice Bob and Charlie do. Now there is a block in the referred paper which ...
5
votes
1answer
43 views

Equivalent determinant condition for Peres-Horodecki criteria

The Peres-Horodecki criteria for a 2*2 state states that if the smallest eigenvalue of the partial transpose of the state is negative, it is entangled, else it is separable. According to this paper (...
4
votes
1answer
57 views

How to find a common eigenstate of commuting operators?

I have multiple different operators in matrix form and I need to find their common eigenstates. The challenge is that the common eigenstate is in a superposition of multiple states and isn't just a ...
5
votes
1answer
39 views

Get result measurement into a circuit with Qiskit

I'm trying to implement the three qubit bit flip code in Qiskit. Therefore, I need to get the result of a measure of two ancilla qubits, to deduce which gate I need to use do recover my logical qubit....
10
votes
2answers
908 views

Is swap gate equivalent to just exchanging the wire of the two qubits?

Is swap gate equivalent to just exchanging the wire of the two qubits? if yes why not just switching the wire whenever we want to apply a swap gate?
2
votes
1answer
44 views

Eliminating a term of a superposition state

Is there a way of eliminating a term of a superposition state? Let's say I have the state $$\frac{1}{\sqrt 2}|00\rangle + \frac{1}{2}|01\rangle + \frac{1}{2}|10\rangle$$ What operation would I do to ...
2
votes
0answers
36 views

Experiments stuck on VALIDATING ibmq_16_melbourne

Since yesterday I'm trying to run on the new composer (quantum-computing.ibm.com) both new experiments (never run before) and older experiments (that have been successfully run and completed some ago) ...
-1
votes
0answers
31 views

IBM Q [Grover's Algorithm]

How to apply the changes on circuit design for Grover's Algorithm n=5 in ibm q ? i Have tried n=3 which is already present there.
4
votes
0answers
35 views

What is the motivation for Weyl matrices in quantum information theory?

Quantum Entanglement and Geometry — Andreas Gabriel (2010) — Sec: 2.3.4 ~p. 11 Another basis for $d\times d$-dimensional matrices that has proven to be quite useful in quantum information theory is ...
4
votes
1answer
27 views

Simulating a 3-local Hamiltonian Term

This may be a fairly basic question, but in Nielsen & Chuang, the following circuit is given for simulating $\exp\left(-i\Delta t Z_1 \otimes Z_2 \otimes Z_3\right)$: which uses an ancilla qubit ...
-3
votes
1answer
39 views

D-Flip Flop in FPGA's as quantum computer [closed]

I believe that there is some way to make a quantum computer by programming an FPGA with the D Flip-Flop. The D Flip Flop uses a square wave as the clock signal and another wave, the data input, that ...
4
votes
1answer
22 views

Quantum fidelity simplified formula while both of the density matrices are single qubit states

I have a question while reading the quantum fidelity definition in Wikipedia Fidelity of quantum states, at the end of the Definition section of quantum fidelity formula, it says Explicit expression ...
7
votes
2answers
118 views

How to program a controlled Hadamard-Hadamard gate?

I'm trying to program a controlled gate as the figure below in Qiskit. Should it be sufficient to separate and control individually the Hadamard gates?
7
votes
2answers
80 views

Quantum channel representation of projective measurement

Let $P$ be a projector and $Q = I-P$ be its complement. How to find probability $p$ and unitaries $U_1, U_2$ such that for any $\rho$, $P\rho P + Q\rho Q = p U_1\rho U_1^\dagger + (1-p)U_2\rho U_2^\...
1
vote
1answer
28 views

Perform quantum gate operations using state vectors and matrices

I am getting confused as to how to perform gate operations using matrices and am hoping someone will help me walk through this example. Say I want to perform a Pauli-X gate on the 3rd qubit in a 3-...
3
votes
1answer
60 views

Quantum Computing Project Inquiry

I am wondering if there is a way to get advice\feedback here about the following: I am about to start a MS physics program. I am interested in quantum computing and my department has the option of ...
1
vote
1answer
85 views

Quantum secret Sharing using GHZ state paper

I am reading a paper on Quantum Secret Sharing Quantum Secret Sharing using GHZ states I have doubts regarding the initial phase of the paper, which are: Let me state what things I read and ...
3
votes
2answers
59 views

Amplitude suppression

On contrary to amplitude amplification, can I do some reflection such that my marked states' probability will vanish (ideally become zero but if there are small residuals also acceptable)? In order to ...
2
votes
1answer
36 views

What is Landauer’s principle?

How does the act of erasing information increase the total entropy of the system? This goes by the name Landauer's principle. Some details are here. Can anyone shed more light on this?
2
votes
0answers
41 views

Grover search for basis states with complex coefficents and multiple marked states

I tried to run Grover's search for basis states with complex coefficients, including the marked basis (complex coefficients because the states are obtained from inverse QFT), but it could not amplify ...
3
votes
1answer
18 views

Obtaining phases of all basis states

I’m wondering that is there a way to separate phases of basis states from the magnitudes (namely putting phases on some new basis states with the same probability magnitude) if the exact values of ...
3
votes
1answer
20 views

Plotting Bloch sphere in QuTiP

Is there anyone who reproduced the Bloch sphere given in the paper QuTiP: An open-source Python framework for the dynamics of open quantum systems by J. R. Johansson, P. D. Nation, Franco Nori? I am ...
2
votes
1answer
28 views

What does “an $n$-qubit array can represent $2^n$ possible array elements” mean?

I read "...an $n$ qubit array can represent $2^n$ possible array elements.." on this post. A classical $n$-bit array can represent $2^n$ possible array elements as well, so I'm confused about the ...
7
votes
2answers
166 views
+100

Clarification of the “Calculations” section of the (HHL09) paper

I am reading this paper entitled "Quantum algorithm for linear systems of equations" and am trying to understand a portion of the algorithm described on page 2 and in more detail in the appendix ...
2
votes
2answers
50 views

How do I write a tensor product of conditional gates in matrix form?

I am writing a program where I need to find the eigenstates of an operator that is a Kronecker product of conditional quantum gates. I am wondering how I would compute this product in matrix form as ...

15 30 50 per page