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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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How to do a Bell state measurement on encoded qubits fault tolerantly?

Experimentally how do you do a Bell state measurement? Is it just a CNOT and a Hadamard and then a measurement in the computational basis? Or is it even simpler than that because it is easy to measure ...
Ian Gershon Teixeira's user avatar
3 votes
1 answer
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Will logical clock cycle time be a limiting factor for quantum computations?

Fault-tolerant quantum computation promises to strongly suppress the errors by scaling up the size of the systems. Right now, different physical implementations of proto quantum computers have very ...
Frederik Ravn Klausen's user avatar
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1 answer
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Why do Surface codes generate so much measurement data?

I read in the Sparse Blossom paper: "A surface code superconducting quantum computer with a million physical qubits will generate measurement data at a rate of around 1 terabit per second". ...
Daniel Mandragona's user avatar
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Is there a term for fault-tolerance of logical gates that depends on the underlying hardware?

Is there a notion of fault-tolerance of logical gates that also accounts for the underlying hardware? If so, how is this notion / term called? An example: A possible choice of logical basis states in ...
qubitzer's user avatar
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What could be intermediate steps towards a fully fault-tolerant quantum algorithm with added value for each step?

Starting from an algorithm without any error correction or detection, what incremental improvements can be made towards fully fault-tolerant encoding and operation? It seems that fault-tolerant error ...
qubitzer's user avatar
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1 vote
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Experimental implementation of addition on a quantum computer

Addition is a basic arithmetic routine, but it has been surprisingly difficult to find a reference that experimentally implements it, despite it existing on various tutorials such as qiskit. Is there ...
shixian105's user avatar
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45 views

How to physically implement a CNOT gate with a photon and a cold atom?

If I have qubits in the same platform (superconducting, photon or cold atoms), the implementation of CNOT gates is relatively well-known. However, if I have a photon and a cold atom, how am I supposed ...
AndyLiuin's user avatar
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2 votes
1 answer
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For QC hardware, is there an usecase/need for higher quality semiconductor crystal?

Is there a requirement for higher-quality semiconductor material? For example, is higher purity required? I could imagine, that the quality of germanium, which is used for some Qubit implementations, ...
Felix's user avatar
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What the stern-gerlach experiment would look like for tensor-product observable?

The experiment says, that having the $Z$ observable and a qubit, we can have outcomes $+1$ and $-1$. Suppose we have more than one qubit, and build an observable like $O = 3Z_1 + 5Z_3 + 2Z_4$. It also ...
HaraldRudobrody's user avatar
8 votes
2 answers
106 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): $$ F(\rho, \sigma) = \text{Tr}\left( \sqrt{ \sqrt{\rho} \sigma \sqrt{\rho}}\right)^2. $$ ...
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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3 votes
1 answer
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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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1 vote
0 answers
44 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 ...
Arthur Strauss's user avatar
1 vote
1 answer
103 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 ...
Marco Fellous-Asiani's user avatar
1 vote
1 answer
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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
136 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
73 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
73 views

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
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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
73 views

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
673 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
92 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
  • 25
5 votes
1 answer
294 views

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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0 votes
1 answer
177 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 ...
WhatsYourIQ192's user avatar
1 vote
1 answer
92 views

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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0 answers
24 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 ...
Nichola's user avatar
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1 vote
1 answer
590 views

Number of qubits in quantum circuits in ibm qiskit

How to find number of Qubits ? ...
Khilesh Chauhan's user avatar
1 vote
0 answers
75 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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0 votes
0 answers
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 ...
Ryan Wang's user avatar
  • 247
0 votes
0 answers
65 views

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
0 votes
1 answer
63 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
  • 121
0 votes
1 answer
91 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. \begin{equation} |\phi\rangle = a|0\rangle + b |1\rangle \end{equation} Why are we interested only in linear ...
QuanTUM's user avatar
0 votes
1 answer
70 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
  • 103
4 votes
0 answers
63 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 ...
MonteNero's user avatar
  • 2,684
1 vote
1 answer
74 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
  • 187
9 votes
2 answers
394 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
215 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
58 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
25 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
147 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
142 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
173 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
  • 85
4 votes
2 answers
275 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
  • 2,346
0 votes
1 answer
320 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
695 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
  • 6,702
1 vote
0 answers
131 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
  • 761
3 votes
1 answer
261 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

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