Questions tagged [state-tomography]
For questions about quantum state tomography, that is, the process of fully characterizing a quantum state from experimental measurements.
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How many observables do we need to confirm a qubit state?
Suppose I have many copies of a qubit in the pure state $\vert\psi\rangle$. How many distinct observables do I need to choose to determine that I indeed hold $\vert\psi\rangle$?
For example, if $\vert\...
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Doing Quantum State Tomography on a custom-made gate with Qiskit Pulse
In this simple example I took the Qiskit CX gate, obtained the pulses' schedule and then tried to do Tomography on that. In theory, everything should run smoothly (I think) but I get this "error&...
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Is there a theoretical method to achieve a positive semi-definite density matrix in QST?
The problem of encountering negative eigenvalues in the density matrix during Quantum State Tomography (QST) is well-explained in this Quantum Computing Stack Exchange post.
However, I am seeking ...
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How to do quantum tomography on a subsystem of 2 of 30 qubits in cirq?
I have a 30 qubit system and I need to do quantum tomography on a subsystem of 2 of its qubit. How can I do this in Cirq?
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State tomography in Qiskit on a subset of qubits of real QPU
Could anyone please explain how should I carry out a state tomography on a real device in Qiskit (version 0.43.2)?
I have access to devices with 127 qubits, but I want to perform a simulation using ...
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In what sense does quantum tomography "determine the state prior to the measurements"?
I have come across the term quantum tomography which, according to Wikipedia, is the
[...]process by which a quantum state is reconstructed using measurements on an ensemble of identical quantum ...
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Use qiskit-experiments StateTomographyAnalysis on data previously recorded without qiskit
I would like to use the analysis capabilities of qiskit, i.e. StateTomographyAnalysis of qiskit_experiments on data that were previously measured on a system not ...
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Qiskit experiments state tomography maximum allowed dimension exceeded for pulse gates
I'm trying to run state tomography on a custom pulse gate (currently just a CR(pi/4) pulse) and any attempt to run it on an IBM backend gives a maximum allowed dimension exceeded error. The code runs ...
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Finding the "dual" basis of an overcomplete basis for Quantum State Tomography
This question is related to this stack exchange post: What does the POVM corresponding to single-qubit state tomography look like?
From what I understand, when we are interested in reconstructing a ...
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Why can't we do pure state tomography using interference with a known reference state?
I am new to quantum tomography, and right now I am trying to understand tomography with pure states. It's my understanding if we have the amplitude magnitudes as well as relative phases, we can ...
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Why we use random state to simulate in tomography?
To simulate tomography, we often chose a random state from the Haar measure. But why? If you have any reference for the specific reason, please let me know.
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Error: cannot pickle '_global_parameters' object while performing state tomography with qiskit [closed]
Qiskit version: 0.44.2
Operating system: 64-bit operating system, Windows 10 Pro
...
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Is there a tight operator frame that is also a POVM?
We define the tight operator frame as a set of operators $\{E_i\}_{i=1}^{n}$ satisfying
\begin{equation}
\sum_{i=1}^n \vert \langle \langle E_i \vert X \rangle \rangle \vert^2 = C \Vert V \Vert_2^2, \...
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Global vs local: global density matrix and all the reduced density matrix
I prepare a $n$-qubit quantum state $\sigma$ whose ideal state is $\rho$, then perform state tomography on all the $m$- qubit reduced states. Ideally, I find that all the $m$- qubit reduced states are ...
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Change of basis on a per vector component level
Suppose we have an $n$-qubit quantum state in the computational basis encoded in a classical blackbox function $f(x)$. That is, with $x \in \{0,1\}^n$ we can query $f$ and get the respective ...
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Qiskit experiments on qiskit IBM runtime [duplicate]
I'm trying to perform a state tomography on a quantum circuit using Qiskit experiments. I was able to perform the tomography on the AerSimulator but have still not been able to do the tomography on ...
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state_tomography_circuits error
I build a QuantumCircuit named qc, I want to generate state
tomography circuits to evaluate fidelity of simulation. I used code,
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How to reconstruct the density matrix $\rho$ from the overlap matrix $T_{a,a'}={\rm Tr}(M^{(a)}M^{(a')})$?
Suppose we have $N$-qubit POVM
$${\bf M} = \{M^{(a_1)} \otimes M^{(a_2)} \otimes \cdots \otimes M^{(a_N)}\}_{a_1, \ldots, a_N}.$$
Given an $N$-qubit state $\rho$, the measurement outcome ${\bf a} = (...
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How to improve the state fidelity of state tomography in qiskit
I want to simulate state tomography on a 8 qubit state. I use the example https://qiskit.org/ecosystem/experiments/manuals/verification/state_tomography.html as a guide.
My problem is that I get a ...
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Alternatives to process tomography and gate set tomography
I need to characterize an unknown 2-qubit operation. As I understand it, quantum process tomography (QPT) can do this, but will not account for state preparation and measurement (SPAM) errors. On the ...
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What are the estimate-estimate and estimate-project algorithms for quantum overlap?
In this paper on improvements to the traditional SWAP test to measure quantum state overlap (or fidelity), they mention two methods called estimate-estimate and estimate-project.
I googled about these ...
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How to sample from a unitary 2-design?
How do we actually go about sampling from a unitary 2-design? Because the size of the 2-design grows quickly with the number of qubits, it seems challenging to sample.
Some of the references I've ...
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How are mixed states given to a quantum algorithm?
I've been reading this paper about quantum fidelity estimation, but really have no idea what's going on when it comes to density matrix notation. In the abstract, they have the following quote:
...
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Can you reconstruct some $N$-qubit entangled state only from ($N$-1) qubits?
Imagine that I have a Bell state of two qubits. If I can produce many copies (always of the same state) but I am allowed only to measure one of the qubits, I would be able to tell that the two qubits ...
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Is tomography of the Choi state sufficient for channel tomography?
Given that there is an isomorphism between quantum states and quantum channels (the Choi-Jamiolkowski isomorphism) and given that state tomography is well-researched, why is quantum process or quantum ...
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Problem with qiskit only accepting ${\rm tr}(\rho^2)=1.$ while performing state tomography
I am performing state tomography after a computation cycle in order to store information about the state before measurement and use that information to re-initialise the state for the new cycle of ...
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Basic import problem for qiskit_experiments module, how to fix?
I'm trying to make use of the qiskit_experiments module but I always get a "No module named 'qiskit_experiments'" error while trying to import it. I've uninstalled and reinstalled qiskit in ...
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Qiskit state_fidelity not accepting my Density Matrices
I'm attempting to use qiskit's state_fidelity(state1, state2, validate=True) but keep getting the following error: QiskitError: 'Input quantum state is not a valid'
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Using Qiskit State Tomography on Subsystems
I have a version of the following circuit set up.
...
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What is optimum method for measuring the probability for all zero state given an arbitrary circuit using ancilla qubits and additional gates
Given some arbitrary quantum circuit, I want to measure the probability amplitude for the all zero state in an optimum manner, given possibly additional ancilla qubits and by applying additional ...
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State tomography on a subsystem of the GHZ state
Premise: I am not sure whether I am missing something theoretically.
Given a circuit creating a GHZ state over 3 qubits, say q1, q2 and q3. If I do not consider q3 and perform a state tomography over ...
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Error with StateTomographyFitter
I am trying to perform a state tomography over a circuit of 5 qubits named circ.
I personally measure qubits 1,2 and 3. While the tomography is over qubits 0 and 4. ...
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Prove $\beta=\Lambda\otimes\Lambda$, where $\Lambda=\dfrac{1}{2}\begin{bmatrix}I&X\\X&-I\end{bmatrix}$ for single qubit tomography
In the Section on single qubit quantum process tomography, Box 8.5, Page 393, Chapter 8, Quantum Computation and Quantum Information by Nielsen and Chuang, and in Prescription for experimental ...
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Why is $\chi$ not uniquely determined by $\sum_{mn}\beta_{jk}^{mn}\chi_{mn}=\lambda_{jk}$?
The mathematical construct of the Quantum process tomography is given in Page 391, 392, Chapter 8, Quantum Computation and Quantum Information by Nielsen and Chuang, as follows
Let a fixed set of ...
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Expansion of multi-qubit density matrix in the Pauli matrix basis
The single qubit density matrix can be expanded as
$$
\rho=\frac{tr(\rho)I+tr(X\rho)X+tr(Y\rho)Y+tr(Z\rho)Z}{2}
$$
which can be shown as,
$\rho$ is a positive operator with $tr(\rho)=1$, ie.,
$\rho=\...
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Ensemble state identification from ensemble state distinction
I am trying to derive Fact 5. in paper 1:
Let $\mathscr{E}=\{\sigma_1,.., \sigma_m\}$ be an ensemble of quantum states in $\mathbb{C}^n$. If there is a POVM $\mathscr{M}$ for the state distinction ...
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Why is state discrimination possible to infidelity $\delta$ using $n=\Theta(1/\delta)$ states?
In (Haah et al. 2015), in the first section, the authors study the asymptotic behaviours of fidelity and trace distance between $\rho^{\otimes n}$ and $\sigma^{\otimes n}$ for some given pair of ...
glS♦
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State tomography with Pauli basis measurements for a high number of qubits
My end goal is to recover the quantum state in its computational basis or reduced density matrix of a high number qubit circuit in a real QPU. Taking into account that the number of qubits will be ...
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What is the difference between the complexity $O$-notation?
For a rank $r,d\times d$ density matrix $\rho$, where $d=2^n$, using $O(rdlog^2d)$ measurement settings can reconstruct the density matrix, while I see another description that we need $\Omega(rd\ \...
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How is a quantum state copied for tomography?
The no-cloning theorem prevents creation of independent copies of a quantum state.
And if we use CX gates we create entangled copies, which are affected by each others measurement.
So, how does one ...
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What is the rank of the pure state?
Consider pure or nearly pure quantum state, is it usually low-rank? Can you give a example of a concrete state and its rank?
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IBM Quantum Lab - Server unavailable or unreachable. Would you like to restart?
In the following circuit, I want to perform tomography on the qubits 0,1,2,3 after qubits 4,5,6,7,8,9 are measured.
I run the circuit using with measurement gates on qubits 4,5,6,7,8,9 with the ...
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Quantum process tomography, non-trace preserving
Consider an unknown quantum process, i.e., a black box, acting on a physical quantum system described by a density matrix $\rho$ associated with a d-dimensional Hilbert space $\mathcal{H}$.
A complete ...
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When perform tomography, do I get back to the classical information $\alpha_1,\alpha_2,\beta_1,\beta_2$ that I embedded in qubit?
Imagine I have a classical data(normalised to fit qubit) in the form of$\alpha_1,\alpha_2,\beta_1,\beta_2$ I assumed data to be in qubit
$$\left| \psi \right> = (\alpha_1 + i\alpha_2 ) \left|0\...
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What are the best-known lower bounds on the number of measurements required for quantum state tomography?
I'm very curious to know more about bounds of number of measurements (or number of independent copies of state) required to reconstruct full density matrix $\rho$ such that it is $\epsilon$-close (...
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Optimising state tomography for fully entangled states
As tomography methods are usually inefficient, it's interesting to find good approximation.
I was wondering the following:
Assume one wants to estimate a state $\rho$ on $n$-qubits.
Given a basis of ...
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Do quantum states with a single parameter give any theoretical or experimental advantage compared to multi-parameter ones?
If a quantum state is a single parameter two-qubit mixed entangled state then is there any theoretical or experimental advantage compared to a multi-parameter state?
suppose, we take a single ...
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Quantum State Tomography Implementation in IBMQ
I am working to understand quantum state tomography, specifically using the algorithm presented in PRL 108, 070502. This paper is referenced in IBMQ implementations of QST, both in old deprecated ...
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Is it possible to efficiently measure outer products of quantum states, of the form $|a\rangle\langle b|$?
I am looking at a matrix reconstruction algorithm that, given singular values $\sigma_i$ and quantum states $|u_i\rangle$ and $|v_i\rangle$ that are efficiently prepared on a quantum computer, ...
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How to find the Kraus operators from the process matrix?
I am trying to find the Kraus operator from process matrix.
For instance, suppose that for single qubit identity gate, I have the following process matrix:
...
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