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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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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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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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
34 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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68 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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1answer
65 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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63 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
84 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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1answer
44 views

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
87 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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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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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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1answer
58 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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1answer
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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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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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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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Which type of quantum computer is explained by spin-boson Hamiltonian?

In a review paper of decoherence-free subspace(DFS) [1], they consider the spin-boson Hamiltonian and they write the system of qubits could be the spins of N electrons trapped in the periodic ...
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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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1answer
258 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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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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1answer
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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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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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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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2answers
120 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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194 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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1answer
198 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
170 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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1answer
193 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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2answers
98 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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1answer
148 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: ...
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Computation and measurement of readout error in IBM quantum experience

If p(1|0) (p(0|1)) is the probability that a detector registers 1 given that the actual state is 0 (registers 0 given that the actual state is 1), I guess that the readout error should be computed as ...
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2answers
195 views

Readout error in IBM quantum experience processor

Is there a section on the IBM website that shows information about the readout error for the devices of quantum experience? I have only seen the errors for single-qubit (U2) and CNOT gates but nothing ...
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1answer
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Error parameters from Qiskit backends

In order to build a custom noise model in Qiskit Aer, I requested the error parameters from different backends and got 3 (9) parameters for each single-qubit (two-qubit) gate as output. However, I ...
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1answer
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What is the precise definition of the environment a qubit lives in?

The book An Introduction to Quantum Computing (section 10.4.1 Error Models for Quantum Computing) by Phillip Kaye, Raymond Laflamme and Michele Mosca states the following: Errors occur on a qubit ...
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How can I obtain the lineally independent Kraus operators for the composition of two quantum channels?

Imagine we have two quantum channels, the bit flip and the depolarizing ones (for the corresponding noise models). These two quantum channels have 2 and 4 Kraus operators, respectively. We could ...
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1answer
155 views

Different QFT results when using Simulator or Quantum Machine

I'm performing QFT using the following code: ...
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2answers
280 views

Mitigating the noise in a quantum circuit

I'm using Qiskit and I have a Quantum Circuit (say, circuit) that gives reasonable results when using the simulator, namely ...
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2answers
96 views

Explicit form for composition of Choi representation quantum channels

Let $|\Omega \rangle$ be the maximally entangled state over a bipartite system whose parts are each dimension $d$, i.e. $$ | \Omega \rangle \equiv \sum_i^{d}| ii \rangle $$ Then one way of writing ...
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50 views

Why are two qubits gates more noisy?

I would like to understand why two qubit gates are generally more noisy. If I am interested in single qubit gates, I can have an effective modelling as a master equation: $$\dot{\rho}=\frac{1}{i \...
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1answer
101 views

IBM Q calibration parameters

If I download calibration of a quantum processor on IBM Q website I see these parameters: T1 T2 frequency (GHz) readout error single qubit U2 error rate CNOT error rate T1 and T2 are relaxation and ...
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1answer
93 views

How do I know in which state the qubit is in each step of the circuit for the simulator in qiskit?

I would like to know how to know in which state a qubit is (I am talking about single-qubit errors), because in order to apply a non unitary gate in the simulator I have to renormalize the state or ...
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0answers
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Dealing with noise in NISQ

I wanted to know if there are some way in NISQ (we run "bare" gate without Q.E.C) to certify if an algorithm will give a correct or wrong answer based on the process of a single gate ? For example in ...
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1answer
142 views

How does qiskit finally implement a noise model?

I have been reading qiskit documentation for hours and I still don't get how does it implements noise in the circuit. I have understood that it works with a objects of the class QuantumError which ...