8

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 a set $s_i$ photons is output in each mode $i\in\{1,\ldots, N\}$ where $\sum_is_i=M$, is $$ P_s=\frac{|\text{Per(A)}|^2}{s_1!s_2!\ldots s_M!}. $$ So, indeed, ...


7

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 useful or interesting to try and do so, but rather that it is in some sense more of a practical than a fundamental necessity. I think you yourself put up a good ...


6

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 uncountable. The quantum computing paradigm based on this Hilbert space is called continuous-variable (CV) quantum computing, and a lot of different protocols and ...


6

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 specifically, if the input state is a single photon in each of the first $n$ modes, and one is willing to draw an arbitrary number of samples from the output, then it is ...


6

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 enough they allow tunnelling between them and effectively couple those two modes. Note that the squeezing is necessary in this case (for example, had we used ...


5

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 described by a probability distribution, then the system is classical. Otherwise, it is non-classical. In alternative terminology, for a classical system, people ...


5

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 quantum circuits for multiple qubits unless you have single photon sources and detectors. Alternatively, you could use current cloud-based devices. The IBM Q ...


5

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't know about any of the others so research them yourself rather than taking a product recommendation from me. There are several options and this choice will be ...


5

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 then give a circuit which simulates this using qubits. $\def\ket#1{\left\lvert#1\right\rangle} \def\bra#1{\left\langle#1\right\rvert}$ The three-polarising-...


5

There are various ways in which one or multiple photons can be used to encode qubits. Potentially the most widely used encoding (at least when quantum communication is assumed to within the scope of 'quantum computing' for this question) is the polarization-encoded photon. Here, a single photon is used as a qubit, where two orthogonal polarization directions ...


4

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, as this is a photonic system, potentially qudits) in the system. KLM: A photon as a qubit The first thing that most people think of in terms of photonic qubits ...


4

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 a little arrow pointing somewhere doesn't matter. The fact of that matter is that for an electron spin, having the two possible states "up" and "down", we ...


4

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 $$| \psi \rangle = \alpha | 0 \rangle + \beta | 1 \rangle$$ where $|\alpha|^2 + |\beta|^2 = 1$. The basis $| 0 \rangle$ and $| 1 \rangle$ can be viewed as two orthogonal polarization directions. Bloch sphere is ...


4

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 $<B|racket|S>$. 2- The company Phase Space Computing markets electronic kits that simulate quantum gates and simple quantum algorithms.


4

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 of literature on the subject: as soon as one can prove the Boson sampler acted correctly, it is indeed a regime where the Boson sampler can be efficiently ...


3

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 the setup, but you can get a pretty reasonable demo of polarization-encoded BB84 with a few pretty common components: polarized laser pointer some half wave ...


3

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 $$ e^{-i \Delta /2} (a_0 * 1 | 01 \rangle + a_1*e^{i \Delta} | 10 \rangle) $$ which simplifies to $$ a_0 e^{-i \Delta /2} | 01 \rangle + a_1 e^{i \Delta /2} | 10 \rangle $$


3

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 you've specified and, indeed, people frequently do.


3

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. Now you ask what the probability of getting the outcome 1 from the final measurement, depending on whether or not the second measurement device is present.


3

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 can indeed be encoded into an internal degree of freedom; for instance the polarization of the photon. However, there are plenty of other systems where the ...


3

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 single-photon detector, here). A polarizing beam splitter might send horizontally polarized photons in one direction and vertically polarized photons in another....


2

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 realised with linear optical elements. This cannot be done with 100% efficiency. However, there are schemes that allow it to work in a heralded way, i.e. it ...


2

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 circuit, if a single photon was input, the output would produce a state in a decaying superposition of subsequent time bins. If you choose a temporal basis for ...


2

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 with time-bin encoding (e.g. 1706.06312). Another example that comes to mind is Silberhorn's group in Paderborn. They use time-bin encoding for various things, a ...


2

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 there though!


2

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 $c_{k,l}$ are baryocentric coordinates. You can then match with the previous more general definition of $\rho_d$ term by term on each of the $c_{k,l}$. The inequalities ...


2

You seem to be thinking about "quantum memory" like it is one specific thing and there is only one specific way it can happen. In reality, what you describe is a valid notion of quantum memory. Another popular one, involving the element Yb, is this one: https://arxiv.org/abs/1701.04195.


2

Here is a handful of Linear Optical Quantum Computation (LOQC) resources I have found useful in the past: "Linear Optical Quantum Computing" (2005) by Kok et. al.: this is probably the best review paper that came out after Knill, Laflamme, and Milburn's 2001 discovery that theoretically-efficient LOQC was possible. It's a pretty thorough but very accessible ...


2

a good stater i would say is the paper of Knill and Laflamme about LOQC (Linear Optical Quantum computing) from 2001, that says that quantum computing can be achieved with linear optic. Photons are really good as they can be used in many way to create qubits (polarisation of course, but also time, frequency, OAM). A Ph.D Thesis of Laurent Olislager is ...


2

Intraphoton entanglement uses the degrees of freedom from one photon only to create entanglement. So, here either polarization and linear momentum or polarization and angular momentum can be used to create entanglement. Interphoton entanglement is the entanglement created between 2 spatially separated photons. So, naturally latter is less stable than former. ...


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