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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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): $$ F(\rho, \sigma) = \text{Tr}\left( \sqrt{ \sqrt{\rho} \sigma \sqrt{\rho}}\right)^2. $$ ...
Frederik Ravn Klausen's user avatar
3 votes
1 answer
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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 ...
John Doe's user avatar
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2 votes
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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 ...
John Doe's user avatar
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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 ...
Arthur Strauss's user avatar
2 votes
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How does one realize quantum gates on actual quantum devices?

I am interested in understanding the process of implementing quantum gates on actual quantum hardware such as those developed by Google, IBM, and others. My current understanding is that each hardware ...
user185671631's user avatar
1 vote
1 answer
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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 ...
Marco Fellous-Asiani's user avatar
1 vote
1 answer
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 ...
user2820579's user avatar
5 votes
1 answer
119 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 ...
Marco Fellous-Asiani's user avatar
1 vote
1 answer
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 ...
EFH's user avatar
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When did Rigetti release their 128-qubit chip?

On Aug 6 2018, Rigetti announced that they would release a 128-qubit chip within a year. They provided an update on Jan 24 2019, but there is no mention of further progress. Other sources all mention ...
Medulla Oblongata's user avatar
1 vote
1 answer
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Phase accumulation for multiple Rabi driving pulses

When a single-qubit gate is operated by Rabi driving, the resulting operator is equivalent to $$ \hat{O} = R_z(\omega t) R_x(\Omega t)\tag{1}$$ where $\omega$ is the frequency of the driving field, $\...
jackphen's user avatar
1 vote
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non-variational formulation of imaginary time evolution

I was wondering if there is a codebase online or if somebody here has implemented successfully the non-variational formulation of the imaginary-time evolution algorithm in qiskit. I know ...
Manas Sajjan's user avatar
1 vote
0 answers
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In qubit phase tracking, does the phase $\delta$ have to be synchronized to the Larmor precession?

In many textbooks (e.g. LaPierre 2021 or Byrd 2022), when dealing with the physical implementation of quantum gates in spin qubits, Larmor precession is usually introduced first as a way to rotate the ...
jackphen's user avatar
1 vote
1 answer
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How to create a electron in a superpositon?

I am trying to understand how are qubits created and implemented in real life. I was unable to find much information about how electrons are kept or sent into a superposition of our wish which is of ...
D Star Let's Explore's user avatar
5 votes
2 answers
450 views

What is the clear definition of coherent versus incoherent errors?

The noise types in quantum computing are pivotal topics frequently discussed in academic papers. Could you provide a clear definition of coherent versus incoherent errors? Additionally, I'm keen to ...
Yunjie Wang's user avatar
2 votes
0 answers
90 views

Superconducting charge qubit and Cooper pairs

In the superconducting charge qubit implementation of the qubit what I've understood is that we read a 1 if a Cooper pair has gone through the Josephson Junction into the "island" and we ...
Omeglac's user avatar
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1 answer
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Rabi amplitude in theory vs practice

I am a bit confused with the definition of Rabi amplitude and how it relates to experimental values. If I understand correctly, we can show a rabi driving (waveform) with the following formula: $\...
Rex's user avatar
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1 answer
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Qudits in NISQ Devices: Benefits Beyond Dimensional Advantages?

It's clear from foundational research that qudits can provide an enhanced control of the Hilbert space over qubits, and I've encountered references that highlight improved robustness and noise ...
banercat's user avatar
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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 ...
WhatsYourIQ192's user avatar
1 vote
1 answer
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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 ...
Saber's user avatar
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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 ...
Nichola's user avatar
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1 answer
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Number of qubits in quantum circuits in ibm qiskit

How to find number of Qubits ? ...
Khilesh Chauhan's user avatar
1 vote
0 answers
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 ...
Ryan Wang's user avatar
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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 ...
Ryan Wang's user avatar
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Physical interpretation of superposition state

I was confused with interpreting superposition state in the anharmonic energy diagram. In the anharmonic energy diagram, an energy pulse can shift the state of the qubit from $|0\rangle$ to $|1\rangle$...
Amey Meher's user avatar
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1 answer
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.
P.A.M's user avatar
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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 ...
inq's user avatar
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1 answer
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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. \begin{equation} |\phi\rangle = a|0\rangle + b |1\rangle \end{equation} Why are we interested only in linear ...
QuanTUM's user avatar
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0 answers
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 ...
Cody Payne's user avatar
0 votes
1 answer
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 ...
Volpina's user avatar
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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 ...
MonteNero's user avatar
  • 2,501
1 vote
1 answer
62 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 ...
Will Yang's user avatar
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9 votes
2 answers
377 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 $\lvert 0\rangle \otimes \lvert \psi \rangle$. ...
Andrea's user avatar
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3 votes
1 answer
198 views

Quantum and DNA computing

Recently I came across the article Associative Quantum Memory. In the article, the authors discussed early physical implementation of quantum computers with NMR. In particular, NMR implementation used ...
Martin Vesely's user avatar
2 votes
1 answer
54 views

Randomness and precision of Quantum Number Random Generators

I am reading about the problem of generating random quatum numbers, and I am interested in the state of the art in terms of the true randomness these generators achieve. As far as I know, following ...
Martin Hurtado's user avatar
1 vote
0 answers
23 views

How does superconductivity quantize the (non-)harmonic oscillator of the LC-circuit?

When reading literature on transmon, or in general charge, superconducting qubits the explanation usually starts from why two metallic islands with a bridge can be seen as LC-circuit, how that is a ...
qcabepsilon's user avatar
4 votes
0 answers
121 views

Probability of error in BB84 if Eve is using Breidbart's basis

I'm taking a course on quantum cryptography and I have a homework to calculate probability of error in BB84. The task says to assume that Eve uses the Breidbart basis with eigenvectors $$|φ_0⟩ = \cos(...
demonsrun's user avatar
2 votes
2 answers
122 views

Physical interpretation of a 2-photon-qubit system occupying the antisymmetric Bell state

This question regards the reconciliation of QIT with what I have learned separately in lectures about quantum physics. My understanding is that indistinguishable bosons are always described by ...
symmetry-question-haver's user avatar
1 vote
2 answers
154 views

How to measure an unknown state produced by a source of qubits?

What kind of experiment can allow me to measure an unknown state produced by a source of qubits? For example: the state of photon polarization. But it can be another one. I have no information about ...
Dimitri's user avatar
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4 votes
2 answers
264 views

Is quantum energy teleportation a specific version of quantum teleportation?

I just read another sensationally titled article in Quanta magazine, Physicists Use Quantum Mechanics to Pull Energy out of Nothing where they discuss the work of Masahiro Hotta on transferring energy ...
Mauricio's user avatar
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0 votes
1 answer
271 views

Hamiltonian in CNOT gate implementation

I am studying the physical implementation of the CNOT gate from "Introduction to Quantum Computing" (Ray LaPierre) and I am confused about the order of operators in the tensor product of the ...
random person's user avatar
7 votes
3 answers
657 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 ...
Tristan Nemoz's user avatar
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1 vote
0 answers
121 views

Detuning in Rydberg blockade Hamiltonian

I am reading the mechanism of the Rydberg blockade as a quantum gate. For a two-atom system with Rabi frequency $\Omega$, detuning $\Delta$ and blockade potential $V$, the system Hamiltonian is given ...
Yunzhe's user avatar
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2 votes
1 answer
221 views

Logical vs Physical Qubits for Quantum Chemistry DFT

How many physical qubits are required per logical qubit in a typical Density Functional Theory implementation for a large number of atoms?
user23301's user avatar
4 votes
0 answers
195 views

What are currently the best reported qubit error rates per gate operation?

Based on some investigation, I have found the best qubit coherence timescales, in superconducting architectures, to be the order of milliseconds. https://journals.aps.org/prb/abstract/10.1103/PhysRevB....
user111's user avatar
  • 173
3 votes
1 answer
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Do quantum loops exist?

I was checking the book from Nielsen and Cheng and they mention in chapter 1, page 23, that quantum circuits don't have loops: "There are a few features allowed in classical circuits that are not ...
neilson's user avatar
  • 209
1 vote
1 answer
234 views

The physical realisation of a quantum oracle [duplicate]

I am having doubts about the physicality of the quantum oracle used in the quantum search algorithms. The standard definition of the search problem (e.g Nielsen and Chuang) states that we are ...
Adrien Amour's user avatar
1 vote
1 answer
342 views

Changing the phase of one qubit is equivalent to changing the phase of another qubit. What is the physical interpretation of this?

Given two qubits, let's say it's in state $|01\rangle = |0\rangle \otimes |1\rangle$. These two qubits are not entangled. Applying a $\theta$ angle phase change (sorry if this is the wrong terminology)...
Theemathas Chirananthavat's user avatar
1 vote
1 answer
80 views

Physical qubit estimates when using surface codes

I've been trying to recreate physical qubit requirements to attack elliptic curve cryptography for the good people over at cryptography stack exchange. I don't want to get too deep into the arcana of ...
Daniel S's user avatar
  • 143
1 vote
1 answer
261 views

Where does 1/sqrt(2) come from in the state of i

I’m trying to learn about calculating coordinates for $\theta$ and $\varphi$ in a Bloch-sphere. I came accross this book about it, including example questions. At question 2.12b, they ask to give the ...
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