10
votes
Accepted
What components are needed to realize a photonic CNOT gate?
Contrary to DaftWullie's answer, it is possible to implement a CNOT gate in a photonic system with 100% efficiency.
However, there are caveats to this - it depends on what's used as the qubits (or, ...
- 3,647
9
votes
Is it possible to "calculate" the absolute value of a permanent using Boson Sampling?
It appears to be true, up to a point. As I read Scott Aaronson's paper, it says that if you start with 1 photon in each of the first $M$ modes of an interferometer, and find the probability $P_S$ that ...
- 54.4k
8
votes
Accepted
How are two photons entangled in the Xanadu computer?
QML researcher at Xanadu here.
Our X-series chip produce entangled states by squeezing light and then combining it at beam splitters: those 'cables' are waveguides in a chip, which when they are close ...
- 196
8
votes
Accepted
Does a photonic quantum computer control a single photon?
There are various ways in which one or multiple photons can be used to encode qubits.
Potentially the most widely used encoding is the polarization-encoded photon (at least when quantum communication ...
- 5,289
8
votes
Accepted
Is 216 qumodes photonic quantum processor equivalent to 216 qubits superconducting quantum processor, in terms of computational power?
My name is Isaac and I work at Xanadu.
That’s a really good question! Generally speaking, you can argue that 216 qumodes are more powerful than 216 superconducting (SC) qubits since qumodes encode ...
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7
votes
Accepted
What types of quantum systems use infinite values?
You are right, photonic systems are described by an infinite (separable) Hilbert space---the bosonic Fock space---and their formalism makes extensive use of infinite values, both countable and ...
- 483
7
votes
Accepted
What about BosonSampling can be publicly verified?
About the need of boson sampling verification
First of all, let me point out that it is not a strict necessity to verify the output of a boson sampler. By this, I don't mean to say that it is not ...
glS♦
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7
votes
Is it possible to "calculate" the absolute value of a permanent using Boson Sampling?
You cannot efficiently recover the absolute values of the amplitudes, but if you allow for arbitrary many samples, then you can estimate them to whatever degree of accuracy you like.
More ...
glS♦
- 22.9k
5
votes
Do any educational quantum computing toys or devices exist?
Quantum computers are, unfortunately, quite hard to build. Experiments with polarizing filters or beam splitters would be able to demonstrate quantum effects, but I know of no way to make simple ...
- 11.1k
5
votes
Accepted
Do any educational quantum computing toys or devices exist?
You can get the sort of optical bench that is typically used for classrooms.
For a couple examples:
3B Scientific
School Speciality
I think the one I have taught with before was from 3B, but I don'...
- 3,603
5
votes
Accepted
Analyzing the three-polarizing-filter experiment as a quantum circuit
We may simulate the three-polarising-filter experiment as a circuit, in the following way, using qutrits.
I will start by describing this as a sequence of transformations (a channel) on qutrits, and ...
- 11.7k
5
votes
Accepted
What does negative probability represent?
What is non-classicality?
I'm not sure if there's a universally accepted definition, but the way that I'd define it is: if all possible outcomes of experiments on a particular quantum system can be ...
- 54.4k
5
votes
Accepted
How is the polarization of a photon able to hold quantum information?
Firstly, that sphere that you've pictured is convenient for thinking about what's going on, but remember that it is not what is actually happening. So the fact that you don't visualise light as having ...
- 54.4k
5
votes
How is the polarization of a photon able to hold quantum information?
In quantum theory, the pure states are associated with the unit vectors of the Hilbert space. A pure state of a quantum bit can be represented as
$$| \psi \rangle = \alpha | 0 \rangle + \beta | 1 \...
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4
votes
Do any educational quantum computing toys or devices exist?
Here are a couple of contributions related to your question:
1- Very recently, Chris Ferrie created an open-source card game based on a toy version of quantum mechanics, called $<B|racket|S>$.
...
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4
votes
What components are needed to realize a photonic CNOT gate?
The original question was asking with respect to a particular Quantum Game. This quantum game only contains the elements of linear optics, not all optics, so it was basically asking how CNot can be ...
- 54.4k
4
votes
What about BosonSampling can be publicly verified?
Just a small complement to @gIS excellent answer: I know of several people (including myself) interested on the public verification aspect. As far as I know, all attempts have failed, hence the lack ...
3
votes
Accepted
Implementing BB84 protocol with easily-obtained consumer hardware
I am glad you enjoyed my experiments! :) I'd be happy to talk more about how I ran that project --- dm me at twitter.com/crazy4pi314.
To your question, I don't know of any good papers or articles on ...
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3
votes
Analyzing the three-polarizing-filter experiment as a quantum circuit
Consider a sequence of 3 measurement devices, applied sequentially to the same qubit, which starts in the 0 state. The first and last devices measure in the Z basis. The second measures in the X basis....
- 54.4k
3
votes
Accepted
Phase shifter acting on double rail states
Start in
$$
a_0 | 01 \rangle + a_1 | 10 \rangle
$$
Then apply $P \otimes I$ to get
$$
a_0 * 1 | 01 \rangle + a_1*e^{i \Delta} | 10 \rangle
$$
But that is the same up to phase as
$$
e^{-i \Delta /...
- 3,603
3
votes
Accepted
Multi-photon states in photonic quantum computing?
Yes. The kets themselves can have arbitrary labels, and it's just for you to establish the connection between them and the physical scenario. There's no reason why you can't have the physical scenario ...
- 54.4k
3
votes
Accepted
Do photons also suffer from decoherence?
A comment said that the most common way to encode q information in photons is using their internal degrees of freedom, not using a "there/not there" encoding.
When using photons, quantum information ...
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3
votes
Accepted
How is measurement performed on a stream of polarized photons?
One idea is to do polarimetry. By using a polarizing beam splitter, the polarization qubit can have each of its polarization components directed to a different detector for photon counting (ideally a ...
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3
votes
How big is the Hilbert space of a boson sampling experiment?
It was frustrating to read that Wikipedia page. Rather than explaining every single problem with it, I'll only mention the top three problems in the single paragraph that you quoted (if there's this ...
- 13.4k
3
votes
Are there practical uses for boson sampling?
There is a number of techniques that use Gaussian boson sampling for approximate solution of some practical problems:
https://iopscience.iop.org/article/10.1088/2058-9565/ab8504/meta
For example, some ...
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3
votes
Accepted
What is the optimal hardware for quantum computing, and what factors contribute to its preference?
The short answer is the field is very much undecided.
The longer answer is the ideal quantum computing hardware is whatever can run a useful quantum algorithm that solves a classical intractable ...
- 1,360
2
votes
Accepted
Photonic Circuit Idea (Does this already exist?)
To answer your first, general question: Optical circuits are usually drawn with a selection of conventional symbols, a directory of which to draw them can be found here.
With respect to that specific ...
- 1,616
2
votes
Time-bin encoding qudits
There is a number of groups using time-bin encoding to realise computation/communication protocols.
One example is Furusawa's group in Japan, which among other things works on measurement-based QC ...
glS♦
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2
votes
Accepted
Time-bin encoding qudits
Yes! The first application of time bin photonic qudits that comes to mind is for quantum key distribution. Here's an example: https://arxiv.org/abs/1611.01139. I am sure there are more references out ...
- 36
2
votes
What are the ranges of the four $q$ parameters in the magic simplex of Bell states formula?
It looks like the only relation they say is $\text{IdentityMatrix}[3^2]=\sum P_{k,l}$.
You get a linear combination of $P_{k,l}$. Those are vertices of a $d^2-1$ simplex so the coefficents $c_{k,l}$ ...
- 3,603
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