Questions tagged [noise]

For questions about different types of noise a quantum computer (or qubits) may experience; how this affects the outcome of the computation; how to reduce a specific type of noise on a specific implementation of quantum computer; or how to simulate noise.

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Mitigating Noise and teleportation

Is it possible to use the mitigation process on a teleportation circuit? Sorry, i'm still starting, if someone can get me out of this doubt, I would appreciate it. The circuit I'm trying to make this ...
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Is noise the only reason that makes the results of Quantum Support Vector Machine (QSVM) and Classical SVM differ, when we use a large dataset?

When I used and tested out the Quantum Support Vector Machine for just 120 samples of a large dataset (Training - 100 and Testing - 20). Its kernel classification results were quite close to the ...
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If there is quantum noise, can a time interval be short enough that only one-qubit errors (eg. as in the Shor code) occur?

The Shor code can be used to protect against an arbitrary one-qubit error. If the time interval over which quantum noise acts is short enough, can it be assumed only one-qubit errors occur, so one ...
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40 views

unexpected effect of coherent unitary error in qiskit

I'm trying to simulate the effect of a coherent unitary Z rotation at an arbitrary angle of a single qubit on the fidelity of a quantum circuit. I am using the qiskit Aer noisy simulator. More ...
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77 views

Noise-induced amplitude amplification?

I wanted to share some results from an experiment which I find thought were deeply surprising. The basic idea is to prepare a superposition in a main register then conditionally apply lots of random ...
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316 views

How are eavesdroppers detected when using BB84 in the presence of noise?

I would like to expand upon this question: What is the probability of detecting Eve's tampering, in BB84? Let's say that when the receiver (colloquially referred to as Bob) receives a qubit and ...
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2answers
166 views

Determining whether there exists an equivalent set of unitary Kraus operators

I have a CPTP quantum channel $\mathcal{E}$ that I've characterized by an operator sum representation $\{E_i\}$ for $i=1, \dots, m$ which acts on an input state like $$ \mathcal{E}(\rho) = \sum_{i=1}^...
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How do you quantify the figurative 'cost' of a quantum circuit

Many gates are not available on a real computer and therefore the circuit must be transpiled into a specific set of gates. I have seen this equation below which is used to to determine the 'cost' of a ...
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What are examples of Kraus operators describing the process of control error?

Noise, such as photon loss or dephasing, is often described with Kraus operators. Are there examples of Kraus operators describing the process of control error?
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understanding final state of a QPU interacting with the environment

As stated in UT's QML course for a QPU that is interacting with the environment: The environment is defined by a temperature $T$, and if we let the system equilibrate, the QPU will become thermalized ...
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How to turn a 'term' in a QuantumError into a QuantumError?

A QuantumError class may have many terms, and we can use .error_term(position) to have a look at each term. But it returns a list instead of another QuantumError ...
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1answer
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Graph States subjected to finite erasures

The appendix to the paper Graph States as a Resource for Quantum Metrology states that when graph states subjected to finite erasures, $$G\Rightarrow Tr_\vec{y}G.$$ While more explicitly he explains ...
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Iterative Phase Estimation with noise vs standard Quantum Phase Estimation with noise

I am doing Qiskit Lab 4 about Iterative Phase Estimation. I created a circuit implementing IPE for theta = 1/3 (phase of 2pi/3). Here's the circuit: It seems to do okay if I run it without noise in a ...
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125 views

Can quantum error correction work on any type of channel?

It says on wikipedia that quantum error correction can (at best) correct phase flips and bit flips. A popular form of representing a quantum channel is in its Kraus representation (scroll down to ...
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51 views

noisy circuit by openfermion

I am working on designing quantum error mitigation algorithms for simulating chemical systems. Therefore, a necessary component is to add noisy to the ideal circuit when using a quantum simulator. But ...
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Is un-computing $U$ a good proxy for circuit fidelity?

I'm trying to estimate the fidelity of some family of unitaries $U(\theta)$ implemented on a noisy quantum computer. To do so, I start from an uninitialized state $|0\rangle$ and run the circuit $U(\...
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1answer
56 views

How can I fit an unknown quantum channel?

Suppose that I have one noisy channel $\mathcal{E}$ and I want to fit it with another one $\mathcal{E}_0(p)$ that depends on some fitting parameter $p$. As both of this processes for me are ...
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85 views

Qiskit: simulate a circuit using a backend noise model

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79 views

What are the possible gates that I can use to vary input states before CNOT?

We know that the noise of the $\text{CNOT}$ gate varies depending on the input state before it. What are the gates that I can put in the place of the 4 identity gates above to change the input state ...
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1answer
58 views

Is Noise model for quantum prototypes accurate in Qiskit

We know that in Qiskit noise models modeling specific quantum machine prototypes exist and can be inserted into the code. However, are these models fixed in nature or they continuously improve ...
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1answer
81 views

Depolarization of density operator with zeros in diagonal

I suppose a quantum state with density matrix like the following is not valid. $$ \begin{bmatrix} 0 & 1 \\ 0 & 0 \end{bmatrix}. $$ Now, let's say I have a valid density operator representing ...
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82 views

Why and how is quantum noise predictable?

I have been learning about quantum error correction using the zero-noise extrapolation method from this paper and have been pleased with the results. This method takes advantage of the fact that the ...
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1answer
91 views

Bernstein-Vazirani Gate IBM Q Noise

When running the attached Bernstein-Vazirani gate on IBM Q, with 1024 shots on ibmq_16_melbourne, I receive the expected result of "00110" with 26.563% success. I notice that there is a lot ...
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2answers
123 views

How to intentionally add noise to a Qiskit circuit?

I am attempting to intentionally add noise to my qiskit circuit by applying n-pairs of CNOT gates. The effect of this should be to yield the same result of my baseline (no pairs of CNOT gates applied) ...
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Bit Flip, Seperable state and Several Question about Cirq

1)I want to use noise model for my state and bit_flip is not defined on cirq. ...
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1answer
89 views

Simulating noise of googles quantum computers

Is there a way to simulate the noise of googles quantum computers using circ? In the same way that any of IBM's computers can be simulated using different backends? ...
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112 views

Simulation of Noise in a particular quantum computer

I wish to be able to model a quantum computer with all the noise sources of an IBM quantum computer. For a given set of T1, T2, readout_errors, U2_errors and CNOT errors I want to know how to include ...
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56 views

Why is the VQE insensitive to noise?

I was going through the Grove documentation on the Variational Quantum Eigensolver. In one of the demonstrations with noisy gates, it is seen that resulting eigenvalue is quite close to the expected ...
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72 views

What do the "gate errors rates" mean physically for IBM's quantum computers?

I wish to simulate the gate errors from IBM's various quantum computers. However I am not sure what the gate error rate physically means. An error rate of say 0.01 for a particular means one in every ...
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60 views

Noise model for 3 Qubit $|GHZ \rangle$ state measurement circuit

I found this example code in Qiskit documentation. Does this code signify that it is simulating noise as per the IBM Valencia quantum chip. If yes, what kinds of noise does it simulate? I executed the ...
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47 views

How can I implement a circuit that simulates white noise on $n$ qubits?

I want to test an error model of the convex form $$t \times \text{ideal_state} + (1-t)\times \text{noisy_circuit}.$$ In terms of density matrices, this would look like $$t\rho_{\text{idealState}}+(1-t)...
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30 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,...
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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 ...
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Do we expect similar results in form of measurement histogram for both (1 run with 100 shots) and (100 runs with 1 shot each)?

100 runs of 1 shot each were executed one by one over a single qubit initialised with 0 (default) and no quantum gate implemented on top of it. All measurement results were found to be noise free i.e. ...
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Qiskit function phase_amplitude_damping_error

I am reading about the noise models that can be simulated in Qiskit and I found out the phase_amplitude_damping_error function. I read about it and it seems to be a function that simulates a combined ...
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475 views

Is there any way we get the state vector/density matrix of a noisy simulation in qiskit?

In Qiskit we can't use noise models in the 'state vector_simulator' or the 'unitary simulator', hence making it impossible to compute fidelity of the output of the noisy circuit and the noiseless ...
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There seems to be a bias against states with more 1s, in IBM's calibration matrix generator: What are the consequences and possible solutions?

Qiskit's function CompleteMeasFitter builds a calibration matrix in this way (2 qubit case): Everything is initialized in the state $|00\rangle$, which is the ...
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3answers
128 views

Is spontaneous excitation possible?

I know the $|1\rangle$ state can relax spontaneously to the $|0\rangle$ state, but can the opposite also happen?
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How does noise affect the implementation of quantum gates?

I am trying to think about quantum noise visually here. If, for example, one wants to implement an X-gate to perform a 180-degree rotation around the Bloch Sphere. In a perfect world, the X-gate will ...
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3answers
86 views

In the three-qubit bit flip code, why can the first bit flip without impacting the entanglement with the other qubits?

The principle of the three-qubit Bit Flip Code is straight forward at first sight. Using CNOT you basically encode $$a|0\rangle + b|1\rangle $$ to $$ a|000\rangle + b|111\rangle$$ using ...
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A question about quantum noise model

Now, I try to understand some concept of Quantum Noise Model and Quantum Channel. The Quantum Noise can be represented as a quantum operator with their own probability. As far as I concerned,(I dont ...
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25 views

Frequency collision and crosstalk error

As the number of qubit increasing, the frequency of qubit will be crowded and there will become the frequency collision. I was wondering that is there any relation between frequency collision and ...
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128 views

Why should we use density matrices to simulate quantum systems with noise?

Why we should use density matrices to simulate quantum systems with noise? I found that the any QEC circuit is included by some quantum gates just like normal cases, which means the state vector can ...
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254 views

Why attenuator and not filters for QC driving line

In all the cold quantum computer designs (superconducting qubits, spin qubits) attenuators are put on the driving lines. Their role is to kill the noise spectral density that comes from higher ...
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296 views

I want to create a depolarizing channel on IBM qiskit

I want to replicate the depolarizing noise channel for a 4 qubit circuit system, where p is the probability for an error. I tried doing this: But I get the error ...
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2answers
260 views

Prove that the depolarizing channel is completely positive

In two dimensions, for a density operator $\rho$ and probability $\lambda$, a depolarizing channel can be written as: $$\mathcal{E}(\rho) = (1-\lambda) \frac{\mathbb{I}}{2} + \lambda\rho$$ In ...
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290 views

How to not optimize the quantum gates in a qiskit circuit when running it in the real device?

I have been trying to run two circuits in the ibmq_london device, the one resulting of applying one X gate on qubit $0$ and the one that applies two X gates. I know that applying two X gates is the ...
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115 views

What happens when you send a Bell state through depolarizing channel?

For noise parameter $Q$ and a density matrix $\rho$, we know that the depolarization channel $\mathcal{E}$ would act like: $$ \mathcal{E}(\rho) = (1 - Q)\rho +Q\frac{I}{2}, $$ where $I$ is the ...
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218 views

Exponential Growth of Noise in Quantum Computers

I recently listened to a presentation for Introductory Quantum Computing. It was very general and meant to give the listeners an idea about the potential for Quantum Computing. The speaker ended the ...
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QAOA with Qiskit: Is the initial state affected by the noise model?

I'm doing a simulation of the QAOA algorithm with noise via the QAOA class of Qiskit 0.19. Here's (part of) my code: ...