The Quantum Firestorm
The Quantum Dragon (feat. IQT News) Exclusive
DC Comics’ Firestorm is a superhero with a very interesting attribute. He is actually formed from the fusion of two individuals, one of whom controls the body while the other communicates with him, kind of like an interactive sixth sense. Appropriate for quantum, Firestorm can change atomic structures, thereby transmuting elements.
Q-CTRL recently published “Achieving computational gains with quantum error correction primitives: Generation of long-range entanglement enhanced by error detection,” which fuses two distinct protocols: teleportation and error detection. The result, like Firestorm, is a singular, more capable protocol.
Teleportation
What do you do when you have a large, superconducting quantum chip, and you want to use quantum information currently on one end of the chip to perform computation on the other end? Do you do a bunch of SWAPs, accumulate all those errors, and celebrate measuring sheer noise? No, of course not.
What do you instead is create a large GHZ state, disentangle all the qubits in the middle, leaving you two distant entangled qubits. You then teleport the quantum information across the circuit. No error-loving SWAPs needed.
There’s one little catch, though. The process of creating those distant entangled qubits is also wrought with errors. Gosh darnit, what are we going to do now?
Well, we’ve got the body of Firestorm. We need to add that smart guy that’s supposed to be guiding him.
Error Detection
You know what happens when you entangle and disentangle qubits? You actually create syndrome qubits, which are used in quantum error correction (QEC). We can detect errors on our data qubits by measuring these syndrome qubits, and we can then use this information to correct errors, as needed, on our data qubits.
Unfortunately, we’re not all the way there yet. Full QEC requires tremendous resources in terms of qubit counts, number of operations, time of execution, and so forth. These resources are either not available at all, which is usually the case, or using them introduces an amount of noise that overwhelms any information gain they might provide.
Fortunately, Q-CTRL’s protocol takes us a step in this direction. We can use mid-circuit measurements to at least detect errors. We can’t correct them and enjoy fault tolerance, but we can know that errors occurred while creating this distant entangled pair. We can get those measurement results back and disregard the errant ones.
With today’s hardware, we’ll probably be discarding a non-trivial percentage of the results. But if we run our circuits enough times – not an impractical number of times, by the way – we can end up with a non-trivial count of results with which errors were not detected. It’s not fault-tolerant quantum computing (FTQC), but we can improve the results we get with the hardware we’ve got until the day comes that we can do even better.
And just to be clear, the overall protocol is not limited to teleportation protocols; that part of the protocol is actually just an example. Appropriately, the character who becomes Firestorm’s body has indeed changed in different storylines. However, the other half of Firestorm, the one we’re associating with the error detection protocol, has remained constant.
Cost
Throwing around arbitrary percentages, the cost of this approach depends on the error rate. If we run 10,000 shots and discard 50%, for example, we’ll have approximately 5,000 shots that we won’t discard. If we want to keep 10,000 shots, we’ll have to run 20,000 shots. We can then calculate the cost of running 20,000 shots instead of 10,000 shots. The higher the discard rate, the more we’ll have to pay to compensate. That said, we’re paying to improve the quality of our results.
It’s worth noting that wherever Q-CTRL’s Fire Opal is compatible, we can use it to suppress errors and bring down the discard rate, thus saving us a few dollars, euros, or whatever. Although Fire Opal supports mid-circuit measurements, it does not yet support dynamic circuits, so it would not be applicable if you actually want to implement a teleportation protocol.
Applicability
This approach applies to all systems with limited connectivity but that allow mid-circuit measurements. The likely providers are IQM, Rigetti, OQC, and IBM, but this could also apply to Academia. The error detection could even be applied without using mid-circuit measurements, but mid-circuit measurements are preferred. Final measurements allow the syndrome qubits to sit idle for a while, during which time errors can manifest.
It’s important to note that this protocol does not apply to neutral atoms or trapped ions, because those modalities enjoy all-to-all connectivity. Qubits can become entangled and physically move around to perform computation with other qubits elsewhere.
Conclusion
You may be wondering, if we can detect and discard errors, why our results wouldn’t be perfect. The oversimplified answer is that detecting errors can introduce errors. The goal is not to be perfect, because that’s just not possible. The goal, like Firestorm, is to produce a sum that’s greater than its individual parts. The goal is to maximize the value that we can get today by detecting and discarding the errors that we can, which leaves us with fewer errors in our final results.
"Firestorm Confirmed for Injustice 2!" by AntMan3001 is licensed under CC BY-SA 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/2.0/?ref=openverse.