Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

Questions tagged [quantum-control]

For questions about quantum control, the study of theory and methods related to driving quantum systems along target dynamics or states.

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Does quantum control allow to implement any gate?

Using quantum control techniques it is possible to control quantum systems in a wide range of different scenarios (e.g. 0910.2350 and 1406.5260). In particular, it was shown that using these techniques it is possible to implement gates like the…
glS
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Does control and target matter in the CZ (Controlled-Z) Gate?

IBM Quantum Experience and other Algorithm Creators generally draw the CZ gates like this: Does it not matter which qubit is the control and which is the target? If so why?
Jadon Erwin
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Does the Lie closure of a set of Hamiltonians describe all unitaries you can generate with them?

Suppose we have $k$ Hermitian matrices $H_1, ..., H_k \in M_d(\mathbb{C})$. Define $\mathfrak{g} = \langle iH_1, ... iH_k \rangle_{\text{Lie}}$ to be the Lie algebra generated by these Hermitian matrices (i.e. the vector space spanned by these…
Alexey Uvarov
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How do you produce an algebra from a set $\{H, H_i\}$ via commutation?

In a paper I am reading, it states: For open-loop coherent controllability a quantum system with Hamiltonian $H$ is open-loop controllable by a coherent controller if and only if the algebra $\mathcal{A}$ generated from $\{ H, H_i \}$ by…
John Doe
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Do individual qubits on IBM quantum processors share the same control unit?

I want to investigate the maximum possible parallelism of quantum operations on a specific IBM device (such as the latest heavy-hex architecture), which requires a basic knowledge of their control electronics. I want to know whether individual…
jojo
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What is the difference between quantum control and quantum optimal control?

In the context of quantum control theory, it is common to see references to both quantum control and quantum optimal control (e.g. 0910.2350 or the guide on qutip quantrum control functions). Sometimes it seems like the two terms are used…
glS
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Is gate optimization of superconducting qubits really a reinforcement learning problem?

There has in several scientific articles related to designing gates for superconducting qubits, been proposed to use reinforcement learning to design pulses with high fidelity and short duration. Some of the…
psturm
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How to obtain control and drift Hamiltonians for device in Qiskit?

I would like to play around with Qiskit OpenPulse and the publicly available IBMQ quantum computer that supports OpenPulse. My humble goal is to use Qutip's optimal control libraries to get a pulse and feed that into OpenPulse. However, even through…
RustyBamboo
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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?
narip
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Deriving Bloch vector $dr$ from master equation

I am trying to derive the Bloch vector $dr$ for a measurement of a observable in an arbitrary direction $\theta$. For context this is the setup and derivation I have for continuous measurement along the $z$ axis. The equation of continuous…
Ian
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control gate with 3 inputs, two control and rotation gate

My question is about if there is any way to represent a circuit that take 3 inputs and applies a rotation gate on the third qubit if the first two qubits is similar (has the same state)?
Ebtehal Ali
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Underlying Hamiltonians and pulse level controls of different commercially available quantum computers

My research area is in quantum state transfer, and I am trying to perform a 'proof of principle' that requires the underlying Hamiltonians of quantum systems and the control I can have on these systems using pulse-level controls. For example, for an…
ZacB
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Gate cancellations in Hamiltonian simulation

I'm a bit confused about in which case the two unitary gates in a quantum circuit could be canceled? I'm reading an example in this paper. In the following diagram, Figure (b) is a simplified circuit of Figure (a): I'm wondering if Figure (b) is…
ZR-
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The control phase gate in Quantum fourier transform and the question it brings up regarding control gates in general

I have a question that's arose from reading "Quantum computing explained" by David McMahon. On page 212 there's an aspect of his description of the quantum Fourier transform which I don't understand . He writes that after the Hadamard gate has been…
bhapi
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Feedback control with feedback Hamiltonian vs quantum error correction

I stumbled upon a pretty old paper from 2003 by C. Ahn, H.M. Wiseman and G.J. Milburn. They use quantum control with feedback Hamiltonian to perform error correction. The paper proposes to encode $n-1$ logical qubits into $n$ physical qubits. The…
MonteNero
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