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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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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19 views

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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55 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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11 views

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
100 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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34 views

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
62 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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16 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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104 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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86 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
109 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
109 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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116 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
83 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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64 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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38 views

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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17 views

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
80 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
29 views

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
15 views

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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23 views

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
147 views

Different QFT results when using Simulator or Quantum Machine

I'm performing QFT using the following code: ...
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2answers
210 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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1answer
53 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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43 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
78 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
66 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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24 views

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
93 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 ...
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1answer
74 views

Rigorous definition of phenomenological master equation for decoherence

I need to have a resource in which phenomenological decoherence model are well defined and explained. Indeed, from what I read there are three usual timescales considered to model decoherence of a ...
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1answer
93 views

How is quantum error applied to the qubits?

I am trying to check the way qiskit has the noise implemented. I have read how is this theoretically done using quantum channels (see Nielsen and Chuang chapter 8) and I want to verify if qiskit ...
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2answers
765 views

Building a DIY quantum computer - how to reduce a noise?

I refer to A DIY Guide to Building a Quantum Computer and Researchers advance noise cancelling for quantum computers. With my friends, I would like to build our simplified quantum computer. We are ...
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1answer
231 views

What kind of errors does the master equation in the Lindblad form describe, continuous errors or discrete errors?

I noticed that in page 427 in Nielsen & Chuang's book Quantum Computation and Quantum Information, quantum error correction is possible because errors can be discretized. In other hand, the ...
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55 views

What types of noise are there?

I know this does vary to some extent from implementation to implementation, but I'm looking for broad 'classes' of noise. For example, I know a very common source of noise/error is the environment - ...
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59 views

How's quantum noise and fault-tolerance related to symplectic geometry and geometric quantization?

Gil Kalai often speaks of the apparent connection between symplectic geometry, geometric quantization, and quantum noise. He is known to describe one of his focus areas as: (...) properties and ...
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1answer
56 views

How can I implement a kraus_error in qiskit?

I have successfully run bit_flip_error in Qiskit by function pauli_error, but I can not find how to implement a ...
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1answer
306 views

How good is basic_device_noise_model() simulating the noise in the quantum computer?

Is there any paper or article about the performance of the noise model using basic_device_noise_model()? For example, like the noise model in the code below. ...
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1answer
165 views

How to add noise to existing gates in Cirq?

I would like to add noise to existing gates in Cirq, i.e. to define something like NewGate = cirq.Gate(qubit) followed by ...
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1answer
220 views

How to selectively apply noise in Qiskit simulations?

In Qiskit it is possible to specify noise models to apply to simulations. This allows noise to be defined for certain operations, like measurement or each type of gate. Is it also possible to change ...
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1answer
184 views

Implementing noise model in Qiskit using arbitrary basis gates

Consider the simplified code below. The code creates a quantum circuit and a simplified noise model. When I try to simulate this circuit using the noise model I get error message that the simulation ...
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1answer
111 views

What are the physical reasons behind noise/errors in quantum computers?

We know that the current quantum computers are noisy/error-prone. They are susceptible to gate errors (single qubit and multi-qubit), decoherence (relaxation and dephasing), readout error, etc. I want ...
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1answer
115 views

Implementing noise model in Quantum simulator

I have noticed that a few papers, such as this one, provide models two for typical noise that a qubit encounters during network transmission: Λ is the dephasing channel Λ(ρ) = Pq(ρ) = qρ + (1 − q)ZρZ ...
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1answer
117 views

Derive phase damping quantum operation

I am reading about the phase damping quantum operation on page 384 of Nielsen & Chuang's Quantum Computation and Quantum Information (10th Anniversary Edition). Nielsen & Chuang derived the ...
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1answer
123 views

Degradable channels and their quantum capacity

Note: I'm reposting this question as it was deleted by the original author, so that we do not lose out on the existing answer there, by Prof. Watrous. Further answers are obviously welcome. I have ...
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Implementing a depolarizing channel for 2 qubits on IBM Q

I am trying to use IBM Q to perform the following depolarizing channel on a state of 2 qubits $\rho=|\psi \rangle \langle \psi |$: $$\rho \to (1-\lambda)\rho + \frac{\lambda}{4}I$$ This is within ...
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202 views

Quantum teleportation with “noisy” entangled state

This is actually an exercise from Preskill (chapter 4, new version 4.4). So they are asking about the fidelity of teleporting a random pure quantum state from Bob to Alice, who both have one qubit of ...