Scattershot
Destini Armstrong
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Entangled-photon sources with simultaneously near-unity heralding efficiency and indistinguishability are the fundamental elements for scalable photonic quantum technologies. We design and realize a degenerate telecommunication wavelength entangled-photon source from an ultrafast pulsed laser pumped spontaneous parametric down-conversion (SPDC), which shows simultaneously 97% heralding efficiency and 96% indistinguishability between independent single photons without narrow-band filtering. Such a beamlike and frequency-uncorrelated SPDC source allows generation of the first 12-photon genuine entanglement with a state fidelity of 0.5720.024. We further demonstrate a blueprint of scalable scattershot boson sampling using 12 SPDC sources and a 1212 mode interferometer for three-, four-, and five-boson sampling, which yields count rates more than 4 orders of magnitude higher than all previous SPDC experiments.
Experimental setup for generating the 12-photon entanglement. Six SPDC entanglement sources [as shown in Fig. 1] are pumped by laser pulses with a central wavelength of 775 nm, a bandwidth of 5.5 nm, and a repetition of 80 MHz. Dispersion of the laser pulses caused by YVO4 crystals and BBO crystals is precompensated by four prism pairs. The 24 superconducting nanowire single-photon detectors have an average efficiency of 75% at 1550 nm.
Experimental setup and results for high-efficiency scattershot boson sampling. (a) The signal photons from the same crystal are combined into one path by using the same method illustrated in Fig. 1 and guided into a 12-mode optical interferometer. Here we choose a pump beam waist of 0.8 mm and a two-photon count rate of 0.5 MHz. (b) The measured similarity and distance for the three-boson sampling. (c) Extended likelihood ratio test between the experimental data and simulated distinguishable sampler for the three-, four-, and five-photon experiments. (d) A comparison of the three-boson sampling rate with previous experiments using SPDC and quantum dots. The data points are labeled with their references.
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Back in the days when a lot of people still used faxes as a way to communicate, some of those messages would be important. They would be press releases, local sports results or letters for publication.
Public relations agencies should be on top of this, and the good ones know where to target press releases and how to approach journalists. (Of course, some of the less discriminating PR agencies are responsible for the kind of scattershot tactics I was just discussing, so it's worth checking that yours isn't doing that.)
Every Ship starts out with an initial stock of 3 Scattershot stashed in each of the Ship's Cannonball Barrels. Additional Scattershot can be found inside Barrels (especially Cannonball Barrels), Storage Crates and Rowboat Chests all over the world. Scattershot can also be unloaded from previously loaded Cannons.
Scattershot is mainly used as ammunition for loading up and shooting with Cannons. A Scattershot needs to be loaded inside an empty Cannon before it can be used as ammunition. Once a Cannon is loaded, the player can manually aim the cannon with Directional keys and then Shoot the scattershot with the Primary Use key. As the fired Scattershot's firing trajectory and arc is influenced by the angle of the Cannon and the sailing speed of the Ship, hitting targets with Scattershot requires some practice. Scattershot can be used to damage the Hull and various parts of player Ships and the Hull of Skeleton Ships, to defeat Krakens, Megalodons and anything else with health such as Skeletons, Animals and even Players.There are usable Cannons on every Ship, every Fortress, every Skeleton Ship, most Large Islands, and some on The Glorious Sea Dog Tavern as well as at The Reaper's Hideout.
Because as scientists build out these databases with more and more genomes, from creatures both living and extinct, the number of organisms we can identify from a scattershot examination of a single sample just keeps going up.
Are there any drawbacks to Scattershot BS? Well, Scattershot BS certainly requires more SPDC sources than ordinary BosonSampling does, for the same average number of photons. A little less obviously, Scattershot BS also requires a larger-depth beamsplitter network. In our original paper, Alex and I showed that for ordinary BosonSampling, it suffices to use a beamsplitter network of depth O(n log m), where n is the number of photons and m is the number of output modes (or equivalently detectors). However, our construction took advantage of the fact that we knew exactly which n
Has anyone considered doing some sort of feedback Boson Sampling? I have in mind putting a beamsplitter right before the detector, and probabilistically shuttling photons back to their input channel (possibly even the input channel they originated from in the case of scattershot boson sampling).
Fantastic post. I am looking forward to seeing which of the quantum optics labs does the first scattershot BosonSampling experiment! This post also let me understand BosonSampling better. Thanks for the awesome blog.
Well, a BosonSampling device could certainly be a useful stepping-stone toward a KLM quantum computer (to get from one to the other, you just need to add adaptive measurements). And a KLM QC would be universal, so could certainly factor.
On the other hand, BosonSampling itself has no known cryptographic or number-theoretic applications. (Though, if all you care about is evidence for classical hardness, not usefulness, then the evidence for hardness is arguably stronger for BosonSampling than it is for factoring.)
Possibly a very ignorant question on my part since I know even less physics than I do TCS, but does the experiment have to be done with photons, or could it be done with composite bosons like helium-4?
A great deal of effort has been invested in developing single photon sources for the past 20 years for use in quantum key distribution and linear optical quantum information processing. This work has led to the development of a number of single photon sources primarily using quantum dots in optical cavities, microwave qubits in strip-line cavities, and atoms in microwave or optical cavities. Often these are more of a headache than SPDC, but they do exist.
These sources are not perfect yet; they do not always produce a single photon on demand and sometimes they produce more than one, but the improvement of these sources is a matter of technological matter and not some fundamental physical roadblock. They are currently much better than SPDC as single-photon sources.
(Interestingly these Rumsey numbers re of some relevance to our recent computational complexity discussions over here. Even more interestingly, a recent paper on a D-wave experiment attempts to compute Rumsey numbers)
Dear Jay, good questions! I did not refer to the computational task of BosonSampling but to actually creating 20-levels bosons and a bosonic state for 10-bosons based on 10 by 20 complex matrix. (This is why I said that I expect the same for FermionSampling that can be classically simulated even for 1000 Fermions without difficulty.)
Scattershot BS is a subset of Gaussian Boson Sampling because you can always see Scattershot BS as a Gaussian Boson Sampling where you prepare 2N two-mode squeezed vacuum states, apply a random linear-optics circuit [unitary U(N)] over the odd-number modes and the identity on even-modes, and finally sample the photon-number basis on all 2N outputs. The heralding detectors being simulated by the even-modes detectors.
Given that you are likely to be goaded into doing this about every six months anyway, consider announcing a series of special SO editions on the topic. For example, each Jan 1 and July 1, everyone with a report on the topic can post.
Likewise, in the case of Scattershot BS, if m>>n2 then you can attenuate your SPDC sources to the point where, in a 1-ε fraction of runs, every source produces either 0 or 1 photons. So then distinguishing those cases again suffices (though not to detect the ε fraction of cases where you did get higher-order terms).
But your sentence made me curious: when you seen less than n photons you just discard the run? Does this imply a hard lower bound on the detection efficiency of, say, \(\eta \ge \frac23^\frac1n\)?
This seems to raise another question Is there any unexpected collapse we can show occurs if Boson Sampling is enough to simulate BQP, i.e. something like if one has an oracle O that simulates boson computers in the sense of Theorem 1 from your original paper with Alex Arkhipov, can we then get some unexpected inclusion of the form BQP
It would be wonderful (obviously) if we could induce high-order quantum coherences among individual spins, protect these coherences by means both passive and active, interact them by tunable Hamiltonians, and read them out with high fidelity. After all, individually these capabilities have been demonstrated convincingly; now the great quest is to demonstrate them simultaneously and scalably.
Before moving on to Harvard he came to Waterloo, and we arranged to meet over lunch. He is great to talk to, and of course very knowledgable. To me it seems he approaches D-Wave with unbiased academic curiosity. For instance he originally was sceptical of their chip truly performing quantum annealing, but backed this conclusion in a later paper when the data strongly suggested it.
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