# Questions tagged [experimental-realization]

For questions about physical implementations of a quantum algorithm or other quantum information protocol. DO NOT use for questions about simulation or emulation of quantum computers, or cloud-based quantum computing services like the IBM Q Experience.

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16 views

### Config (setting) file choices for Python

Before raising my questions, I am aware there are similar questions on other websites that have been answered pretty much in very good detail, but I am interested in asking my questions from a quantum ...
43 views

### In what limit does the estimator sample variance converge to the Cramer-Rao bound?

In the context of a single phase estimation problem of a quantum photonics experiment (related post). For example consider a 3-photon quantum circuit (such as the Mach-Zehnder which depends on some ...
85 views

### What is the definition of physical gate error rate?

The fidelity of two quantum states $\rho$ and $\sigma$ is a well-defined (up to discussions about a square): $$F(\rho, \sigma) = \text{Tr}\left( \sqrt{ \sqrt{\rho} \sigma \sqrt{\rho}}\right)^2.$$ ...
1k views

### Why do we have to measure the circuit before sending it to the real quantum computer?

If I want to run a circuit on a real quantum computer, I have to measure it before running it. For example: ...
399 views

### How do I stepwise rotate a qubit on a Bloch sphere using $SO(3)$ and $SU(2)$ group?

Let us first introduce two fundamental functions for coordinate transformations: ...
792 views

### Question about DIY Quantum Computer Prototype

I recently came across these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits). ...
8k views

### Why is it harder to build quantum computers than classical computers?

Is it because we don't know exactly how to create quantum computers (and how they must work), or do we know how to create it in theory, but don't have the tools to execute it in practice? Is it a mix ...
58 views

### Fisher information from likelihood function for discrete quantum case

In the context of a single phase estimation problem of a quantum photonics experiment. For example consider a 3-photon quantum circuit (such as the Mach-Zehnder which depends on some phase shift ...
1 vote
37 views

### Can a single qubit gate fidelity be benchmarked through XEB (Cross-Entropy Benchmarking)?

I'm currently investigating two qubit Cross-Entropy benchmarking and was able to simulate the decay curve that one would get in experiment when doing cycles for the case of two qubits (random single ...
587 views

### What design considerations set the frequency bounds for superconducting qubits?

Superconducting qubits generally have frequencies within the range of 4 - 8 GHz. What design considerations give the upper and lower bounds for what is a feasible design. I.e, why can't they be higher ...
1 vote
199 views

### Why in quantum coin toss, when starting from state $|1\rangle$, we get $|-\rangle$?

I was reading qiskit's text book, there I found that for a Double quantum coin toss, we have negative probability amplitude for $|1\rangle$ state when we starts from $|1\rangle$ state. Link : https://...
157 views

### How do qubits interact to form logic gates?

How do qubits interact to form, say, CNOT gates? There are very few comprehensive explanations of how quantum computing works. They all use obscure metaphors that don’t make sense (like Schrödinger’s ...
1 vote
60 views

### Qiskit result per shot

I want to run a simple circuit with one qubit and a hadamard gate on a Quantum Machine. I want the result of every shot in a list. It works with a simulator and the get_memory function but this ...
1 vote
101 views

### Example of two-level systems which has very long lifetime "in nature" but as soon as we manipulate them their lifetime is very small

I am looking for examples of quantum systems which could serve as qubits (electron spin, electrical levels of ions, whatever) that verify the following properties: In nature they can have very long ...
297 views

### How many physical qubits are needed to encode a logical qubit on ion trap, superconducting, neutral atom, photonic QC?

How many physical qubits are needed to encode a logical qubit on an -- ion trap, -- superconducting, -- neutral atom, -- photonic, -- spin quantum computer based on today's technologies?
1 vote
42 views

### What do the numbers mean in the elements used in ion traps?

Sorry for the dumb question. Some ions used in quantum computing are Yb171+, Be9+, Ca43+. According to this ionic numenclature, "We have seen that some elements lose different numbers of ...
120 views

### What are the limitations of Harvard's and Google experiment on quantum error-correction

I am currently reading the papers about the QEC (quantum error-correction) experiments of 2023 and while they are impressive (!), I would like to better understand what are their limitations. My goal ...
1 vote
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1 vote
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### What is complete structures of the photonic quantum computers?

I am interested in studying quantum computers based on photonic integrated circuits. I am looking for a site, article, book, or material that will introduce the process of its implementation step by ...
689 views

### How are elementary quantum gates realised?

When expressing computations in terms of a quantum circuit, one makes use of gates, that is, (typically) unitary evolutions. In some sense, these are rather mysterious objects, in that they perform "...
988 views

### What is entropy quantum computing?

Recently there is news concerning some computational breakthroughs by using so-called "entropy quantum computing": https://thequantuminsider.com/2022/07/20/qci-solves-3854-variable-problem-...
210 views

### How to design a RF-SQUID qubit by Qiskit Metal?

I am now learning how to use Qiskit Metal to design superconducting circuits. I found that there are only several transmon qubits in the library. Can I design an RF-SQUID qubit by using Qiskit metal? ...
22 views

### What is the closest experimental platform to $H=\sum_{ij} J^X_{ij}X_iX_j+J^Y_{ij}Y_iY_j+J^Z_{ij}Z_iZ_j$?

Consider the Hamiltonian $$H=\sum_{ij} J^X_{ij}X_iX_j+J^Y_{ij}Y_iY_j+J^Z_{ij}Z_iZ_j$$ where $X,Y,Z$ are Pauli spin operators and $J_{ij}^\alpha$ are arbitrary couplings that can be positive and ...
1 vote
408 views

### Number of qubits in quantum circuits in ibm qiskit

How to find number of Qubits ? ...
1 vote
66 views

### What's the difference between Superconductor, Photonics, and Nuclear Magnetic Resonance implementation of the physical QC?

I'm a bit new to Quantum Computing and I wonder why organisations are using different physical architecture. I realise that any physical implementation can be valid as long as it uses the fundamentals ...
33 views

### What level of physics and math do I need to get into Quantum Computing (hardware)?

I already understand the abstractions of Quantum Computing (software), which includes qubits, interference, qubit entanglement, and circuits. However, despite being able to write Q# code that makes up ...
194 views

### Measuring Ising anyons: What is a fusion measurement?

I have several doubts about measuring Ising anyons. Measurement is crucial for quantum computation and even more so for magic state distillation which is necessary to make Ising anyons universal. ...
10k views

### How does a quantum computer do basic math at the hardware level?

On reading this Reddit thread I realized that even after a couple months of learning about quantum computing I've absolutely no clue about how a quantum computer actually works. To make the question ...
58 views

### Is there any recent review on the state of the art of NMR quantum computing?

Is there any recent review on the state of the art NMR quantum computing? there are some reviews but they are not complete. for example does not give the data for the gate times and so on.
16 views

### quantum mechanical outcome of heating an ensemble of particles

Following the post in our neighboring chemistry community, I would like to understand the expected outcome when an ensemble of particles at their ground state is heated to gain additional energy ...
88 views

### Why are we only interested in the linear combination $|\phi\rangle = a |0\rangle + b |1\rangle$?

They say superposition enables qubit to live in linear superposition of two states. I.e. $$|\phi\rangle = a|0\rangle + b |1\rangle$$ Why are we interested only in linear ...
33 views

### What would be the simplest physical implementation of a CNOT operation between spin and energy DoF's?

I'm working on a project where I'm considering a two-level system ("atom" for convenience) which possesses two linearly independent degrees of freedom, one of them a spin degree of freedom ...
58 views

### Quantum algorithms and binomial distributions and probabilities

Qubits in a quantum computer are mostly spins of quantum particles.But since spin can take up to 2 values does this mean quantum algorithms are applied mathematics which make use of binomial ...
62 views

### When is a quantum algorithm considered to have a significantly superior performance over another quantum algorithm?

Suppose we have two heuristic quantum algorithms $A$ and $B$ that attempt to solve a certain class of optimization problems. Let's suppose that the benchmarking metric is Time To Solution (TTS), which ...
1 vote
63 views

### What is the purpose of Doppler cooling in neutral atom devices?

As a theorist without much experimental physics background, I am reading some reviews to understand how these systems work. I've learned that one needs to use Doppler cooling before trapping the atoms ...
381 views

### Does post selection of a qubit introduce non-linearity?

Problem I have a multi-qubit state $\lvert \psi \rangle$ and an ancilla qubit $\lvert 0 \rangle$ that I use to extend my state, getting the new state $\lvert 0\rangle \otimes \lvert \psi \rangle$. ...
666 views

### Does Google's error correction paper invalidate Gil Kalai's arguments?

In his paper "The Argument against Quantum Computers, the Quantum Laws of Nature, and Google’s Supremacy Claims", Gil Kalai argues that quantum advantage will never be reached. For NISQ ...