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Questions tagged [photonics]

It is the branch of physics and engineering concerned with the properties and transmission of photons. Use this tag for those questions about photonics which are relevant to quantum computing.

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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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1 vote
2 answers
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In a QKD protocol such as BB84 how do Alice and Bob deal with lost or undetected photons?

In a quantum key distribution protocol such as BB84 how do Alice and Bob deal with lost or undetected photons in practice? Imagine Alice sends 1001 using X Z X Z bases. Bob then receives 101 (second ...
Omeglac's user avatar
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2 votes
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38 views

Is the choice of Measurement-based model specific to the hardware technology?

Most photonic hardware providers seem to prefer Measurement-based quantum computing (MBQC) over the gate-based model. Is this due to some limitations of the corresponding hardware technologie? If yes,...
26118in's user avatar
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0 answers
19 views

How do photon gates act on ground and excited states?

https://strawberryfields.ai/photonics/conventions/gates.html#displacement The above is the only profile of Photon Gate from Strawberry Fields. I have the following doubts about Photon Gate: Which of ...
Ren-Xin Zhao's user avatar
2 votes
1 answer
56 views

What do the angles in a Poincaré sphere represent?

I understand the principle of the Bloch sphere. You write your state in the following way: $$|\Psi\rangle = \cos(\theta/2)|0\rangle+e^{i\varphi}\sin(\theta/2)|1\rangle.$$ The angles $\varphi,\theta$ ...
Mauricio's user avatar
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Where is my mistake in using a measurement operator instead of Born’s rule to calculate the probability of detecting photons at an arbitrary angle?

As I asked in this question: How can I calculate the measuring probabilities of a two qubit state along a certain axis? From here I know how to calculate the probability of measuring a general state ...
Alex1111's user avatar
1 vote
1 answer
47 views

Two-photon N00N state through Mach-Zehnder interferometer

I am interested in modelling a two-photon N00N state sent through a Mach-Zehnder interferometer, which consists of a beam-splitter (50:50), a phase shift operator on the first mode, a phase shift ...
John Doe's user avatar
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2 votes
1 answer
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What is the best way to model a polarizer?

If I have a photon reaching a polarizer, I can think of a polarizer as an operator of $P=a^\dagger_Va_V$ where $a^\dagger_V$ creates a photon with vertical polarization (V). However, on the other ...
Mauricio's user avatar
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1 vote
1 answer
185 views

Type I fusion Gate

In the type I fusion gate of the Rudolph-Browne protocol, I fail to understand how the detection of a photon means the entanglement of the two Bell pairs.
physics22's user avatar
1 vote
1 answer
91 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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1 vote
1 answer
491 views

What is the optimal hardware for quantum computing, and what factors contribute to its preference?

In conventional computing, the use of CMOS (Complementary Metal Oxide Semiconductor) technology as the foundational circuitry for digital logic gates in CPUs has become the industry norm. CMOS's ...
Max's user avatar
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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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1 vote
1 answer
133 views

How to entangle 2 qubits using a polarizing beam splitter?

A polarizing beam splitter splits a continuous beam of photons in 2 directions: (from here) (from here) I am curious and have a few related questions about using simple optics in quantum computing: ...
James's user avatar
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1 vote
0 answers
575 views

Two-way quantum computers (like in Ising model) - are they possible? Could solve general NP problems? [closed]

Standard one-way quantum computers (1WQC) allow for e.g. Shor, Grover algorithms, however, general NP problems seem too difficult for them(?) - bringing an open question if they could be somehow ...
Jarek Duda's user avatar
1 vote
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44 views

Can one simulate Gaussian Boson Sampling using Fock Boson Sampling or vice versa?

In Fock Boson Sampling, one starts with a particle-number state $|n_1, ..., n_m\rangle$ of $m$ modes, sends it to an interferometer effecting a unitary operation $U$ on the creation operators, and ...
Alexey Uvarov's user avatar
2 votes
2 answers
134 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
2 votes
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25 views

Is there any error correction experimental set-up based on stationary-flying hybrid systems?

In a former question of mine I asked to detail the functioning of a photonic based set-up encoding a quantum state within a Shor code. I would like to be updated on the eventual existence of any ...
Daniele Cuomo's user avatar
4 votes
0 answers
212 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
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3 votes
1 answer
227 views

Are there practical uses for boson sampling?

Boson sampling is a computation that is not doable on classical machines but quite doable on quantum photonic machines. (https://www.researchgate.net/figure/Experimental-results-for-3-and-4-boson-...
James's user avatar
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1 vote
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Simulating light absorption in Photosynthesis through Quantum computing

Basically, I want to simulate the above photosystem process of light absorption. Above is a diagram of laser beams shot into antenna pigment molecules and traveling to the reaction center. Two ...
Levent Ozbek's user avatar
1 vote
0 answers
40 views

CNOT gate path interference

I have a question on paper https://doi.org/10.1038/nature02054. In this paper, the CNOT gate is realized using a beam displacer for higher stability. The figure below shows a 1:1 mapping from (a) to (...
유승연's user avatar
1 vote
1 answer
153 views

What is a "spatially encoded qubit"?

I am studying the photonic CNOT (https://arxiv.org/abs/quant-ph/0403062v1). I am not understanding what is a spatially encoded qubit? How the setup in fig. 1(b) can create this spatially encoded qubit?...
MementoMori's user avatar
1 vote
0 answers
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QuTiP lecture: Single-Atom-Lasing

I have tried to run one of the examples in QuTip lectures: single atom lasing. Although I have used the prepared code represented in reference, I have received error and I have not been able to ...
mehrosadat ebrahimi's user avatar
1 vote
0 answers
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Faithful description of a photonic setting with the circuit model

The above picture comes from this paper. The circuit on the left and the one on the right are equivalent (up to the basis). However, there is an important difference: the circuit makes the input -- i....
Daniele Cuomo's user avatar
3 votes
2 answers
268 views

On the photonic implementation of Shor's code

The above picture comes from this paper. I can see that the standard Shor's code has been re-designed. I have two main doubts: I can't figure out in figure (b) how the setting inputs the state $\...
Daniele Cuomo's user avatar
6 votes
1 answer
404 views

Is 216 qumodes photonic quantum processor equivalent to 216 qubits superconducting quantum processor, in terms of computational power?

Xanadu just launched borealis, 216 qumodes photonic quantum computer, this week. https://xanadu.ai/blog/beating-classical-computers-with-Borealis Its number of qubits is very interesting because it ...
Natchapol Patamawisut's user avatar
1 vote
1 answer
199 views

Gate times for photonic quantum computers

I am trying to understand the landscape of one- and two-qubit gate times for various quantum computing architectures. It is not so hard to find gate times for various gates such as Hadamard, CNOT and ...
Marion's user avatar
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5 votes
1 answer
211 views

How big is the Hilbert space of a boson sampling experiment?

Boson sampling experiments are typically characterized by two key parameters: the number of photons $M$ and the number of modes $N$. A recent experimental demonstration (arXiv:2106.15534) with $M = ...
tparker's user avatar
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6 votes
1 answer
577 views

Does a photonic quantum computer control a single photon?

Does a photonic quantum computer control a single photon and use it to represent a single qubit? I think ion trapped quantum computers use a single ion to represent a qubit. I would like to know how a ...
david's user avatar
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3 votes
1 answer
271 views

How are two photons entangled in the Xanadu computer?

I was recently reading about how Xanadu made a scalable, room-temperature-operating quantum computer using photons as qubits (see this link). It said that in the logic gates, it entangles two photons ...
Blue Herring's user avatar
3 votes
1 answer
286 views

Understanding polarizing beam splitters

I have been trying to understand this heralded CNOT gate on photons but I have some questions regarding polarizing beam splitters: The way I understand it, a PBS lets the photon through if the photon ...
Fateh A.'s user avatar
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4 votes
0 answers
49 views

What is an electro-optic switch?

I found an implementation of a CNOT in photonic QC and I just couldn't find any info on a component named "electro-optic switch" What does it do exactly? How does it work? The ...
Mimo Pakou's user avatar
2 votes
0 answers
33 views

What are the most popular QND measurement implementations used in photonic quantum computers?

What components are used in order to perform QND measurement in photonic quantum computers?
Mimo Pakou's user avatar
3 votes
1 answer
119 views

How is measurement performed on a stream of polarized photons?

Is it possible to use a simple laser to measure qubits in optical quantum computers, or is a single-photon emitter absolutely necessary? If you can do it with a simple laser, how would you go about ...
Mimo Pakou's user avatar
6 votes
0 answers
413 views

Optical quantum computers VS Superconducting quantum computers VS Electron-spin quantum computers

One of the main problems of superconducting quantum computers is that it is necessary to maintain a very low temperature (near absolute zero). Such cooling is very expensive and complex. Why, then, ...
alexhak's user avatar
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2 votes
1 answer
133 views

Design NISQ Circuit with StrawberryFields

I am trying to design this circuits with strawberry fields. However I could not connect my first and second qubit mode: orange boxes are beam splitters, blue boxes are phase shifters. The green box ...
quest's user avatar
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7 votes
1 answer
312 views

Is Gaussian boson sampling (used for showing quantum advantage) a subcategory of the continuous variable approach?

I read about the photonic QC Jiŭzhāng that showed quantum advantage by Gaussian boson sampling. I read that boson sampling itself is a sub-universal technique of QC (where they use single-photon ...
ile2N's user avatar
  • 155
5 votes
0 answers
130 views

How do we realise photonic gates?

I am interested in photonic computing, and I am curious how the gates work. I once saw a picture of a photonic CNOT gate that used just mirrors and polarizers. I have not been able to find any ...
Spock's user avatar
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3 votes
1 answer
161 views

How are Franson Interferometers used to prove security in Photonic QKD Experiments?

I am currently reading this paper about Quantum Key Distribution Protocols which use Franson Interferometers to secure against eavesdroppers. I am having trouble understanding how the interferometers ...
Dunbar Birnie's user avatar
1 vote
1 answer
128 views

Why do we use two optical modes per qubit in the KLM scheme?

The original KLM paper says: The basic states of a bosonic qubit encoded in modes $l_1$ and $l_2$ are $|0\rangle\mapsto|0\rangle_{l_1}|1\rangle_{l_2}$ and $|1\rangle\mapsto|1\rangle_{l_1}|0\rangle_{...
mavzolej's user avatar
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1 vote
1 answer
406 views

How can a half-wave plate affect the position qubit and not the polarization qubit of a photon?

I recently was watching 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). ...
Pranav Jain's user avatar
1 vote
1 answer
65 views

How do we restrict to a limited number of dimensions, say 3 for qutrits, while using OAM states of light?

When a azimuthal phase $\mathrm{e}^{il\phi}$ is applied to gaussian beams having plane wavefront, they develop a corkscrew sort of structure and therefore possess an orbital angular momentum in ...
Devjyoti Tripathy's user avatar
3 votes
2 answers
806 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). ...
Pranav Jain's user avatar
3 votes
1 answer
771 views

Do photons also suffer from decoherence?

In this Question Why do optical quantum computers not have to be kept near absolute zero while superconducting quantum computers do? A comment said that the most common way to encode q information in ...
yousef elbrolosy's user avatar
3 votes
0 answers
88 views

How do I add 1+1 using a photonic computer?

A similar question has been previously asked & has an excellent answer discussing half, full & ripple carry adders. I am curious to find out how these adders would be constructed in the ...
user820789's user avatar
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2 votes
1 answer
460 views

What is infinite squeezing?

I am working my through the Strawberry Fields documentation & the section on state teleportation states: Here, qumodes $q1$ and $q2$ are initially prepared as (the unphysical) infinitely squeezed ...
user820789's user avatar
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3 votes
1 answer
471 views

What types of quantum systems use infinite values?

Background I am curious to learn more about any work that has been done regarding quantum systems that deal with infinite values. I am primarily interested in photonic quantum computing; however I am ...
user820789's user avatar
  • 3,312
6 votes
2 answers
473 views

What are some good resources for learning about photonic qubits?

I am interested in resources that would allow me to learn about the physics behind optical quantum computation, and specifically, the physical properties of photonic qubits. I have some good resources ...
Jack Ceroni's user avatar
5 votes
0 answers
89 views

Are single photons necessary for this quantum autoencoder implementation?

The following diagram is from Experimental Realization of a Quantum Autoencoder: The Compression of Qutrits via Machine Learning How this setup works: What will be obtained from this set up is the ...
Sam's user avatar
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0 votes
1 answer
90 views

What is the difference between "intraphoton" and "interphoton" entanglement?

I am trying to better understand the following: What is the difference between Intraphoton Entanglement and Interphoton Entanglement? I am new in this field and i want to proceed some work on ...
zircon's user avatar
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