3 ms·

This is exciting! But keep in mind that the PR materials can be confusing. If you look at the specs https://www.rigetti.com/qpu https://www.rigetti.com/qpu you

This is exciting! But keep in mind that the PR materials can be confusing. If you look at the specs https://www.rigetti.com/qpu https://www.rigetti.com/qpu you can see their quantum processors have on the order of 10 qubits, and after less than ~10 logical gates the state of the system will be completely scrambled due to the imperfections of the gates. It is a great milestone, and it should be celebrated, but we need something much bigger and way less sensitive to noise to be able to call it "quantum computer".

reikonomusha 8y ago
It should be noted that while quantum computers in this regime don’t outperform classical computers, they still can do sensible calculations. Aside from the toy calculations like producing a Bell state, it seems that the “Hello World” of quantum computing is becoming calculating energies of simple molecular configurations, like dihydrogen. Given that it’s computing something via a bonafide programming language, I don’t think it’s unfair to call it a “quantum computer”.
voiper1 8y ago
How many qubits for useful quantum calculations? What are use cases for quantum computing, that it gives an advantage over regular CPU/GPUs?
- krastanov 8y ago
  The advantage of scalable digital quantum computers when/if they get built is that they can do certain very specific mathematical operations in polynomial time (instead of exponential for classical computers). This is a fairly imprecise statement (but gives good intuition). It is conjectured without yet being proven (still, there are many clues to it being true). It applies only to very specific problems, so there are "classically easy" problems which we will just continue solving with classical computers, and there are many problems that are infeasibly difficult for both classical and quantum computers. An example of where quantum computers will excel is simulating large organic molecules (which is impossible today) ushering a new era of drug discovery and material science. While there are toy applications of small computers, you probably need hundreds or thousands logical qubits. Given the low quality of the hardware and the environmental noise it is expected that you will need to use error correction codes where you encode a single logical qubit on top of hundreds or thousands of physical qubits. In other words, once we have a machine with 10000 physical qubits that can all be well controlled and entangled with each other, with gate fidelities of 0.99 nobody (almost nobody) will be able to argue that it is not a quantum computer. This device here has 20ish qubits with gate fidelities of 0.8 to 0.98.
PascLeRasc 8y ago
This might be a dumb question, but are the logic gates "bare metal" or a software simulation/VM as a proof of concept?
- NathanKP 8y ago
  From what I've read so far they give you both: a VM that simulates qbits for local development, but then you can schedule a real run a physical quantum device (that's the cloud side).

reikonomusha 8y ago

It should be noted that while quantum computers in this regime don’t outperform classical computers, they still can do sensible calculations. Aside from the toy calculations like producing a Bell state, it seems that the “Hello World” of quantum computing is becoming calculating energies of simple molecular configurations, like dihydrogen. Given that it’s computing something via a bonafide programming language, I don’t think it’s unfair to call it a “quantum computer”.

voiper1 8y ago

How many qubits for useful quantum calculations? What are use cases for quantum computing, that it gives an advantage over regular CPU/GPUs?

krastanov 8y ago
The advantage of scalable digital quantum computers when/if they get built is that they can do certain very specific mathematical operations in polynomial time (instead of exponential for classical computers). This is a fairly imprecise statement (but gives good intuition). It is conjectured without yet being proven (still, there are many clues to it being true). It applies only to very specific problems, so there are "classically easy" problems which we will just continue solving with classical computers, and there are many problems that are infeasibly difficult for both classical and quantum computers. An example of where quantum computers will excel is simulating large organic molecules (which is impossible today) ushering a new era of drug discovery and material science. While there are toy applications of small computers, you probably need hundreds or thousands logical qubits. Given the low quality of the hardware and the environmental noise it is expected that you will need to use error correction codes where you encode a single logical qubit on top of hundreds or thousands of physical qubits. In other words, once we have a machine with 10000 physical qubits that can all be well controlled and entangled with each other, with gate fidelities of 0.99 nobody (almost nobody) will be able to argue that it is not a quantum computer. This device here has 20ish qubits with gate fidelities of 0.8 to 0.98.

PascLeRasc 8y ago

This might be a dumb question, but are the logic gates "bare metal" or a software simulation/VM as a proof of concept?

NathanKP 8y ago
From what I've read so far they give you both: a VM that simulates qbits for local development, but then you can schedule a real run a physical quantum device (that's the cloud side).