# Questions tagged [cirq]

A python framework for creating, editing, and invoking Noisy Intermediate Scale Quantum (NISQ) circuits. It is a Python library for writing, manipulating, and optimizing quantum circuits and running them against quantum computers and simulators.

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### Cirq.simulate expectation value of a Hamiltonian

I want to simulate the final state of an ansatz in cirq using simulate. Now I want to calculate the expectation value of a Hamiltonian. How do I do this? I can only find simulator.run examples in cirq....
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### How to learn parameters in a quantum circuit, given an interference pattern?

Using cirq, I have the following quantum circuit, with three parameters: phi, alpha and beta: ...
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### Cirq - Measure Density Matrix Function Getting First Element

Hello I am using measure density matrix function like that: ...
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### Implementing the HHL algorithm with negative eigenvalues (Cirq)

How do I implement the HHL with negative eigenvalues? This paper (https://arxiv.org/abs/1803.01486) says that: what if $\lambda<0$? This problem actually does not hard to solve, since we can ...
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### Cirq-Measuring a State with Rotation Matrix

I have this state: $$p |\text{GHZ}\rangle \langle \text{GHZ}| + (1-p)\rho$$ And after creating this state I have this code lines: ...
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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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### Multiple Bipartite Entangled State in Cirq

I am trying to create this state: rho = = q . rho_{1,2} + r . rho_{2,3} + s . rho{1,3} + (1-q-r-s) . rho_separable And I wrote this code: ...
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### Cirq: Creating an arbitrary gate for an arbitrary number of qubits

How do I create an arbitrary unitary gate for an arbitrary number of qubits in Cirq? Note: A solution for creating a single qubit gate is answered by Thomas W from this post. How do I create my own ...
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### Producing $|ghz\rangle\langle ghz|$ State in Cirq

I could manage to produce 3 qubit ghz state in Cirq. But I don't know how I can produce $|GHZ\rangle\langle GHZ|$ in Cirq Here is my code for 3 qubit ghz state Can you help me please for improving my ...
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### Can I run Cirq on IBMQ?

Google's quantum computer is not yet available for the public. Is it possible to run Cirq on IBM's quantum computers, instead of Qiskit? And if so, how can I do it? Thank you!
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### Output a Cirq gate as a Numpy array?

How do I output a Cirq gate as a Numpy array? For example, I would like to print a Pauli X gate cirq.X as ...
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### Wrong Expectation value when implementing a VQE for the Heisenberg Hamiltonian

I tried to implement an extended Heisenberg-Hamiltonian as an extra exercise further than my homework. My Hamiltonian is the following: $H = \sum_{NN} \sigma_x\sigma_x + \sigma_z\sigma_z$ I try to ...
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### XX and YY and ZZ Hamiltonians in vqe

I'm trying to implement a vqe in cirq and I have sort of a brain knot. I have a 4 qubit chain with periodic boundary condition. So in fact a 2x2 qubit grid. Now 2 of them each are coupled. How do I ...
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### Implementing Cirq Coding Gates

Can someone please help me making these gates on CIRQ programming: Decrement Gate (-1) Splitter Gate (If possible) I was having trouble implementing these and was not sure if it's possible either. ...
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### Running Google Cirq example code from their webpage — where do I find information about PROCESSOR_ID?

I'm just ttrying to run the simple example code in Google's Cirq startup page: https://cirq.readthedocs.io/en/stable/google/engine.html I think I have the access authorized correctly via Google's ...
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### Reordering commuting gates in cirq to reduce circuit depth?

The main functionality for ordering gates in a cirq circuit that I'm aware of is using the predefined insert strategies of cirq.Circuit.insert(). As far as I see, ...
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### Create this state using CIRQ Coding language [closed]

I needed help with CIRQ coding as I'm quite new to Quantum Computing. I read the tutorials on CIRQ but don't really understand it. I'd be very thankful if someone could help. A program to create the ...
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### Deutsch-Jozsa algorithm: an oracle implementation

I would like to implement the Deutsch-Jozsa algorithm myself using cirq. However, I faced the problem of the implementation of the oracle. I endeavored to apply the Deutsch-Jozsa algorithm for $n+1$-...
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### What is the analysis of the Bell Inequality protocol in Cirq's 'examples'?

This question is taken from https://github.com/quantumlib/Cirq/issues/3032. The "standard" protocol measures Alice's and Bob's qubits in different bases, while the one in Cirq measures in ...
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### Applying a gate to all line qubits without explicitly listing them in Cirq

Say we have a custom gate CG, defined by a unitary matrix U, and line qubits qubits in Cirq. ...
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### Visualizing custom gates in Cirq

I'm trying to visualize a custom gate in Cirq. I have through this page, which briefly mentions how to create custom gates in Cirq. However, I'm getting errors when trying to visualize it. My current ...
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### How to build a controlled two-qubit gate?

I have a two-qubit gate with below unitary: ...
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### Can not build circuit unitary for a three-qubit gate in Cirq

I am trying to implement a three-qubit gate in an eight-qubit circuit. The method I use is the same by which I create my two-qubit gates with no issues. I produce the unitary of the gate and then ...
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### Adding Quantum State Tomography Step in Cirq HHL Algorithm Implementation

Over the past month, I have been learning about the HHL algorithm and am interested in extending the implementation provided here (https://github.com/quantumlib/Cirq/blob/master/examples/hhl.py) to ...
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### How to assign values to the symbols in a parametrized Cirq circuit without running it?

Is there a way to use a ParamResolver or Sweep to assign values to the symbols in a parameterized Cirq circuit without running it? For example, something like: ...
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### How to cite cirq in a scientific article?

What would be the best/prefered bibtex entry for citing cirq ? Is this ok ? ...
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### Can We Currently Import Quantum Datasets (Datasets Containing Quantum Data) Onto NISQ-era Quantum Computers?

I'm still investigating the TFQ whitepaper. In one section of the paper, the authors say this with respect to Quantum Datasets In general, [a quantum dataset] might come from a given black-box ...
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### Implementing U2-Gates on Cirq

I am interested in using the QASM2Cirq methods to make this gate: u2(0, np.pi, q). How can I build that object using Cirq rather than QASM string value passed onto cirq.
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### VQE for Beginners : Using Tutorial and Cirq

I have been following this tutorial: https://dkopczyk.quantee.co.uk/vqe/ I am using Cirq to try to teach myself VQE, replicate their results, and also try to understand more about ansatz for ...
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### Placement of quantum circuits

I have a question concerning the placement of quantum circuits on Google devices. Consider the following code: ...
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### A bug during CIRQ installation

I had the following problem with an installation of the Cirq. When I typed python -m pip install cirq, I got the following line: "Cannot uninstall 'sympy'. It is ...
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### Cirq: easiest way to compute qubit Hamiltonian expectation value with number of shots

I was wondering what was the easiest way to take a qubit Hamiltonian, and get an expectation value estimated with a certain number of shots over a parameterized quantum circuit (or ansatz) with Cirq.
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### Building a state with parallel execution

I'm trying to implement the main algorithm described in the Quantum Recommendation Systems paper. In order to do this, I have to create a quantum state $|x\rangle$ corresponding to a real vector ...
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### How to calculate the probabilities of observing quantum states using the “expectation_from_wavefunction” in cirq (and why)

I am currently simulating some quantum circuits, and want to calculate the probabilities of observing each individual state. I am able to use Cirq for this, and calculate it using $P_{00} = |\alpha|^2$...
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### Normalization of the quantum state in Cirq

My understanding, for instance from this youtube video, is the following: Assuming a state $\psi = \alpha |0\rangle + \beta |1\rangle$, where $\alpha$ and $\beta$ can be complex. I believe any state ...
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### Explanation of HHL Cirq implementation [closed]

Can someone help me in understanding the program on the link given below? I would really appreciate if someone could give a detailed explanation ... https://github.com/quantumlib/Cirq/blob/master/...
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### Cirq - Print state of qubit

Seeing a state of qubit is too complicated in Cirq I don't want to simulate, I would be happy for debugging, to see the probability/ amplitude of the state of a qubit, without measure and simulate ...
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### VQE Cirq example

Is my understanding correct that in this example the Hamiltonian measurement is not performed through measuring individual Pauli operators because all its terms are mutually commuting? So, for each ...
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### Understanding SGD on a Quantum Circuit

I implemented the following circuit, a very simple circuit: I applied the technique presented on Farhi's paper - which I am so happy people in here are talking about more and more ! - and applied to ...
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### Ising Model, Graphs, and Cirq

How would you explain, pictorially and without too much overhead, an interaction between the qubits on this model using Cirq? I am interested in trying to map accurately the ansatz on Cirq to a ...
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### Cirq: creating a new device with custom coupling topology?

Cirq has two in-built realizations of quantum hardware, which are realized as GridQubit() and LineQubit() classes (naming convention is slightly disturbing:). GridQubit device mimics connectivity of ...
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### Code for a simple optimization problem in Criq

For a demonstration, I would like to code a simple optimization problem in Cirq. I don't care what the problem is, but I want it understandable to someone who has had only basic algebra. One idea is ...
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### Computing circuit depth in Cirq

I ran into a problem of how to extract circuit depth from Cirq circuit object. In Cirq circuits consist of a list of Moments. Number of moments is not equal to the circuit depth in general case. I ...
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### Moments-based quantum circuit in Cirq

In Cirq, quantum circuit consists of moments, which in turn consists of operations. This is different from Qiskit/OpenQASM, which doesn’t have the concept of moments. What is the design philosophy ...
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### Is there a mistake in the VQE Ansatz in Cirq's tutorial?

I have been going through Cirq's VQE background tutorial and after examining the Ansatz it seems to me that the only layer that actually affects the final measurement is the rot_x_layer. The other ...
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### 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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### cirq.Ry complains that it needs one argument

When I try to put an Ry gate into my circuit in cirq, I get an error saying that it only takes one argument. ...
I would like to prepare the following initial state for variational quantum algorithms:  \sin\theta_1 \sin\theta_2 \sin\theta_3 |000\rangle + \sin\theta_1 \sin\theta_2 \cos\theta_3 |001\rangle + \...