Which in turn requires us to talk about types of network deployments, which don't get enough attention, IMO, though that's improving a little.
Especially, we need to understand that there are similarities and differences between system interconnects or data center networks and wide-area networks.
https://www.osti.gov/biblio/1900586A Roadmap for Quantum Interconnects (Technical Report) | OSTI.GOV
The U.S. Department of Energy's Office of Scientific and Technical Information
It's critical to know that *scaling up quantum computers requires entanglement between quantum processors*. If we want to use two small quantum computers to solve one larger problem, we MUST be able to create inter-node entanglement.
A network of small nodes coupled via an entangling interconnect is what I call a quantum multicomputer. We talked about designs like this in the
#QuantumComputerArchitecture tweetstorm.
https://zenodo.org/records/3496597A #QuantumComputerArchitecture Tweetstorm
A record of a 186-tweet description of the field of quantum computer architecture. This is essentially an annotated bibliography of over 100 journal and conference papers.
It's a MUST, a GOTTA HAVE, a NOT OPTIONAL technology. It's by far the clearest argument in favor of a quantum network.
No entanglement, no scalability.
Beyond that, what about wide-area entangling networks? One of my favorite ideas of the last two decades is blind quantum computation, by Broadbent, Kashefi and Fitzsimons.
https://arxiv.org/abs/0807.4154
Universal blind quantum computation
We present a protocol which allows a client to have a server carry out a quantum computation for her such that the client's inputs, outputs and computation remain perfectly private, and where she does not require any quantum computational power or memory. The client only needs to be able to prepare single qubits randomly chosen from a finite set and send them to the server, who has the balance of the required quantum computational resources. Our protocol is interactive: after the initial preparation of quantum states, the client and server use two-way classical communication which enables the client to drive the computation, giving single-qubit measurement instructions to the server, depending on previous measurement outcomes. Our protocol works for inputs and outputs that are either classical or quantum. We give an authentication protocol that allows the client to detect an interfering server; our scheme can also be made fault-tolerant.
We also generalize our result to the setting of a purely classical client who communicates classically with two non-communicating entangled servers, in order to perform a blind quantum computation. By incorporating the authentication protocol, we show that any problem in BQP has an entangled two-prover interactive proof with a purely classical verifier.
Our protocol is the first universal scheme which detects a cheating server, as well as the first protocol which does not require any quantum computation whatsoever on the client's side. The novelty of our approach is in using the unique features of measurement-based quantum computing which allows us to clearly distinguish between the quantum and classical aspects of a quantum computation.
Maybe the most intriguing thing I have seen in recent years is the combination of quantum computing and quantum sensing, from the group surrounding John Preskill at Caltech, especially the astounding Robert Huang.
https://scholar.google.com/citations?user=2y5YF-gAAAAJ&hl=en
Hsin-Yuan Huang (Robert)
California Institute of Technology, Google Quantum AI - Cited by 4.971 - Quantum Information - Machine Learning - Quantum Many-Body Physics
They have shown how coupling a quantum sensor to a quantum computer *dramatically* reduces the number of times you need to actually run the quantum experiment.
https://arxiv.org/abs/2112.00778Quantum advantage in learning from experiments
Quantum technology has the potential to revolutionize how we acquire and process experimental data to learn about the physical world. An experimental setup that transduces data from a physical system to a stable quantum memory, and processes that data using a quantum computer, could have significant advantages over conventional experiments in which the physical system is measured and the outcomes are processed using a classical computer. We prove that, in various tasks, quantum machines can learn from exponentially fewer experiments than those required in conventional experiments. The exponential advantage holds in predicting properties of physical systems, performing quantum principal component analysis on noisy states, and learning approximate models of physical dynamics. In some tasks, the quantum processing needed to achieve the exponential advantage can be modest; for example, one can simultaneously learn about many noncommuting observables by processing only two copies of the system. Conducting experiments with up to 40 superconducting qubits and 1300 quantum gates, we demonstrate that a substantial quantum advantage can be realized using today's relatively noisy quantum processors. Our results highlight how quantum technology can enable powerful new strategies to learn about nature.
This is one of the most important ideas in recent years, IMO, and it will take us years to figure out all of its implications. It might be used in either a lab+data center configuration, or wide-area setup, it's not clear yet.
All of this work is supported on what, by my estimate, is about 1% of what's being spent on
#QuantumComputing. It's a small but critical part of an entire ecosystem.
Okay, I think that covers what I wanted to say about the utility of entangled networks, both data center and wide-area. Let me also comment on the cookie:
The cookie analogy for entanglement is incomplete, and simplified to the point where it's misleading. Let me see if I can do a little better, but this makes it a LOT longer and murkier, so stick with me...
A cookie has two properties, perhaps flavor (chocolate and vanilla) and shape (round and square), but when you are given a cookie you can't learn about both. You have to pick one.
You can either feel the shape with your hand or you can taste it, but not both, and if you try to look at it instead it just crumbles before you can learn anything about it.
The Quantum Internet is a Magic Cookie Pair Machine. Its job is to make special pairs of cookies and give one to me and one to you.
These pairs of cookies are correlated in a weird way.
You and I ask the Quantum Internet to make a special pair for us. Then we each, independently, decide whether to taste our cookie or feel it, then we share what we found.
Strangely, if we both tasted it, we got the SAME flavor. If we both felt it, we found the SAME shape.
But if one of us tasted it and one of us felt it, each of us just gets a random result.
Of course, if we do this just once, it doesn't tell us much. In fact, we have to repeat this a bunch of times, and what we get is just this weird statistical result.
Until the advent of quantum computing, that's all this was, a weird statistical anomaly, with the profound but esoteric suggestion that quantum mechanics and relativity don't mix.
Nowadays it's critical to the operation of a quantum computer on the inside, but the question at hand is whether it is useful over longer distances. I hope the discussion above gives you some idea of the things we are working to realize.
If you're with me so far, that's roughly the way we use entanglement; taking some combination of the shape and flavor and mixing it with the other qubits at each end to entangle larger sets of qubits. But there's actually a catch in entanglement:
If we just talk about the flavor or shape, well, the cookies might have secretly been shaped & flavored, but we just don't what they are. That would just be classical correlation, not entanglement.
If, instead, we do something odd and measure, well, let's call it flape, not quite flavor or shape. We might find choquare or vacircle.
THEN it turns out that there is still a statistical correlation between the outcomes of the measurements (shape, flavor, flape) at the two ends...in some way that CANNOT be just a hidden characteristic of the already-shared cookies.
This is what John Bell discovered: that there is a statistical test that can prove that the two ends are not completely independent.
Since that discovery in the 1960s, it has been proven with increasing rigor in experiments. I won't go into them here, but search for "loophole-free Bell inequality" if you want to know more.
Ah, did I mention that Clauser, Aspect and Zeilinger won the Nobel Prize in Physics in 2022 for experiments proving the existence of
#QuantumEntanglement?
https://www.nobelprize.org/prizes/physics/2022/press-release/
The Nobel Prize in Physics 2022
The Nobel Prize in Physics 2022 was awarded jointly to Alain Aspect, John F. Clauser and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science"
Yeah, it's weird, and it's not as easy to understand as a broken cookie. Sorry, this is the best I can do without skipping some critical facet of entanglement.
This
#QuantumInternet #QuantumEntanglement thread is more than long enough. Let's finish up.
By now, hopefully you can see that there is an ABSOLUTELY CRITICAL NEED for data center-scale
#QuantumNetworks. There are also Big Science things you can do with a wide-area
#QuantumInternet or with related technology such as LIGO's squeezing.
Whether wide-area entanglement has truly compelling economic uses that will warrant deployment of a new global information infrastructure, well, that's a little harder to see. But would I bet on it? I already have. I've spent a good chunk of the last two decades working on this.
So finally, some references. It won't be a surprise that these are to our own work:
Quantum Communications
The second quantum revolution has been picking up momentum over the last decade. Quantum technologies are starting to attract more attention from governments, private companies, investors, and public. The ability to control individual quantum systems for the purpose of information processing and communication is no longer a theoretical dream, but is steadily becoming routine in laboratories and startups around the world. With this comes the need to educate the future generation of quantum engineers. This textbook is a companion to our video lectures on Overview of Quantum Communications from the Q-Leap Education project known as Quantum Academy of Science and Technology. It is a gentle introduction to quantum networks, and is suitable for use as a textbook for undergraduate students of diverse background. No prior knowledge of quantum physics or quantum information is assumed. Exercises are included in each chapter.
Which is based on the first of three online courses, all uploaded to YouTube, in both English and Japanese: Overview of Quantum Communications, From Classical to Quantum Light, and Quantum Internet.
https://www.youtube.com/@QuantumCommEdu/playlistsBevor Sie zu YouTube weitergehen
Thanks for listening. Hope someone found this interesting, and maybe decides to learn a little more!
And thanks to the brilliant team of several *dozen* people I work with, most especially Shota Nagayama (who leads the Quantum Internet Task Force) and Michal Hajdušek (who does much of the educational materials and most of the physicsing).
@rdviii You deserve a nap, after that one. ;-)
I found it interesting!
Rod Van Meter
Ethan Blanton