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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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If we could only get two-qubit tomography as an output, what algorithms are possible

According to the circuit model, the output for a quantum computation on $n$ qubits is an $n$-bit string. But what if we instead got a full two qubit tomography for all $n(n-1)$ pairs of qubits? This ...
James Wootton's user avatar
6 votes
0 answers
262 views

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 ...
Nathan Miller's user avatar
6 votes
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133 views

Weak Schur sampling and state distinguishability

Consider the task of distinguishing between the following two $n$ qubit quantum states. $$ \rho = \frac{\mathbb{I}}{2^{n}}.$$ $$ \sigma = \frac{1}{2^{n/2}}\sum_{x \in \{0, 1\}^{n/2}} |x\rangle\langle ...
BlackHat18's user avatar
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6 votes
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What is quantum tomography useful for?

First time poster and just started with quantum computing for my master thesis, so I'm sorry if the question seems obvious. I understand that the tomography is used to reconstruct the state and/or ...
Oliver Müller's user avatar
5 votes
0 answers
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What is the best quantum process tomography method?

This question is somewhat related to this question. What is currently the best method for quantum process tomography? By best I mean, the one that can achieve the best accuracy of estimation per qubit ...
Quantum Guy 123's user avatar
4 votes
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57 views

How does the quantum Fisher information provide bounds for the estimation of output states?

Assume you have some quantum process $Q$ (e.g. quantum state tomography) that intakes initialised states $\rho_{i}$, $i=1,\ldots,n$ and gives some output $\rho'_i$. $$ \rho_1 \to Q \to \rho'_1 \\ \...
Marion's user avatar
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3 votes
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Individual processing of quantum circuit measurment results

When superconducting transmon qubits are measured with a readout pulse, the raw readout signal is demodulated, and results appear as clouds on the IQ plane, with one point in the cloud representing ...
psitae's user avatar
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3 votes
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How to quantify trace distance between two matrices representing two quantum optical networks?

This is my first post here, so I'm sorry if this question could be ill-formulated. I have performed measurements on a 12x12 optical quantum network, so that I have a stochastic matrix $P^{exp}$ where ...
v_enushk's user avatar
2 votes
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What is the best method for estimating average channel fidelity?

This thesis shows an efficient way to estimate average channel fidelity (in chapter 4). However, it is somewhat old (from 2005). Are there any better methods out there? By better I mean: are there ...
Quantum Guy 123's user avatar
2 votes
0 answers
94 views

IBMQJob.result() returns KeyError: 'qObjectResult'

I'm running tomography job like I have done many times before. I send the job, and the job.status() is 'DONE'. But when I ask for ...
Andrea's user avatar
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1 vote
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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 ...
Andrea's user avatar
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1 vote
1 answer
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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 ...
Anedar's user avatar
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1 vote
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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 ...
Max Fawcett's user avatar
1 vote
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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 ...
Loic Stoic's user avatar
1 vote
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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 ...
Sooraj S's user avatar
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1 vote
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Confusion about the objective function of VQEs and QAOAs

I am a bit puzzled on how the objective function of the VQEs and QAOAs. Of course, the parametrised state is constructed differently in these two algorithms but they do share a common objective to be ...
Marion's user avatar
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1 vote
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Adding Quantum State Tomography Step to HHL Algorithm (Cirq)

Over the past month, I have been learning about the HHL algorithm and am interested in extending the Cirq implementation to include the quantum state tomography step to extract the amplitudes or ...
quantum_novice's user avatar
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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.
karry's user avatar
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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 ...
Yash Sharma's user avatar
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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 ...
Pratapaditya Bej's user avatar