3 ms·

Again, no. Maybe you're thinking about adiabatic quantum computation, something popularized by D-Wave. But most people in the industry don't call their machines

Again, no. Maybe you're thinking about adiabatic quantum computation, something popularized by D-Wave. But most people in the industry don't call their machines "(universal) computers," but rather "quantum annealers." This is not the same as universal, gate-based computation, which does take an actual program containing instructions, and executes those instructions more-or-less sequentially, just as any computer programmer would expect. The state of the system begins with what is essentially equivalent to a large array of 0's, and you manipulate it accordingly, without resorting to evolution as your primary computational means of marching forward. In fact, left alone, these computers are designed to remain static, like an ordinary computer. (However, they still couple with the environment and decohere, which is one of the major challenges we, as humanity, face in building a useful quantum computer.) This is what Rigetti, IBM, Google, HRL, Amazon, IonQ, ColdQuanta, etc. are doing. They use superconducting transmon qubits, ion qubits, neutral atom qubits, or silicon quantum dot qubits. (There are other companies and qubit technologies still.)

dekhn 5y ago
Hey, um, I think I do know what I'm talking about :). You can see more of this historical side effort, which didn't pan out for a number of reasons: https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_quantum_computer https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_qua... A 7 qubit QC NMR was implemented in 2001. All these systems are just evolution of spin systems or other similar systems. The big difference with an NMR quantum computer is that it manipulates ensembles of spins. The comment about universality of computing is that many physical processes can be used to compute things. I didn't say that qcs were universal computers. Please try to read what i'm writing more carefully.
- reikonomusha 5y ago
  I know what NMR is. The systems are not evolutions of NMR. They're fundamentally different in their design, construction, and physics. An exchange-only silicon dot quantum computer is very different than an NMR quantum computer, which is very different than a neutral atom quantum computer. These computers, these days, are by and large considered computers which execute programs. Perhaps in the 90s-00s that wasn't the case since physicists cared more then about the construction of a laboratory apparatus and less about turning it into a programmable device with program and data I/O. I can't comment on what you know or don't know, but what you're writing is misleading and not accurate. The two points you've made (about what's considered computing and how modern quantum computers work) are what I refute.
  - westurner 5y ago
    "Quantum computing: A taxonomy, systematic review and future" (2022) https://doi.org/10.1002/spe.3039 https://doi.org/10.1002/spe.3039 "Multi-qubit quantum logic operations with ion-implanted donor spins in silicon" (2022) https://scholar.google.com/citations?view_op=view_citation&hl=en&user=_G8qcyEAAAAJ&sortby=pubdate&citation_for_view=_G8qcyEAAAAJ:FPJr55Dyh1AC https://scholar.google.com/citations?view_op=view_citation&h... https://meetings.aps.org/Meeting/MAR22/Session/G39.1 https://meetings.aps.org/Meeting/MAR22/Session/G39.1 (Veritasium video) > Among semiconductor qubits, the electron and nuclear spins of donors in silicon play a special role for their conceptual simplicity (a 31P donor in silicon is similar to hydrogen in vacuum) and their exceptional coherence times [1] and 1-qubit gate fidelities [2]. Here I will present experimental progress on multi-qubit logic operations with donor spins, which point to several credible pathways for scalability using ion-implanted donors in MOS-compatible devices. The current state of the art is a hybrid electron-nuclear 3-qubit processor [3], where two 31P nuclear spin qubits are coupled to the same electron. The shared electron enables a geometric nuclear two-qubit CZ gate, which we perform with 99.37% average fidelity. NMR single-qubit gates reach fidelities up to 99.95%, and state preparation and measurement are performed with 98.95% fidelity. These three metrics show how close this system is to operating at fault-tolerance thresholds. Further, we entangle the two nuclei with the electron to prepare a 3-qubit GHZ state with 92.5% fidelity. Electron-nuclear entanglement unlocks the ability to connect nuclear qubits via the electrons, for instance using exchange interactions [4]. We have operated a weakly (~10 MHz) exchange-coupled 31P donor pair as a 2-qubit electron system, with native CROT gates performed by resonant microwaves. Gate fidelity benchmarks are underway and will be reported at the Meeting. On the engineering side, we have demonstrated the ability to implant single donors in silicon with confidence up to 99.85% [5]. This striking result identifies ion implantation as a scalable and accurate manufacturing strategy for spin-based quantum computers in silicon. QoS: Quantum-on-Silicon The survey article above just says "[Quantum] Output"? Is that different from registers? How long are those states ah coherent? "Researchers store a quantum bit for a record-breaking 20 milliseconds" (2022) https://phys.org/news/2022-03-quantum-bit-fora-record-breaking-milliseconds.html https://phys.org/news/2022-03-quantum-bit-fora-record-breaki... > By managing to store a qubit in a crystal (a "memory") for 20 milliseconds, a team from the University of Geneva (UNIGE) has set a world record and taken a major step towards the development of long-distance quantum telecommunications networks. What are repeaters, and what are [quantum] prepared states in re: registers and longer-term storage for non-collapsed (or just probabilistic?) qubit outputs?

dekhn 5y ago

Hey, um, I think I do know what I'm talking about :). You can see more of this historical side effort, which didn't pan out for a number of reasons: https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_quantum_computer https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_qua... A 7 qubit QC NMR was implemented in 2001. All these systems are just evolution of spin systems or other similar systems. The big difference with an NMR quantum computer is that it manipulates ensembles of spins. The comment about universality of computing is that many physical processes can be used to compute things. I didn't say that qcs were universal computers. Please try to read what i'm writing more carefully.

reikonomusha 5y ago
I know what NMR is. The systems are not evolutions of NMR. They're fundamentally different in their design, construction, and physics. An exchange-only silicon dot quantum computer is very different than an NMR quantum computer, which is very different than a neutral atom quantum computer. These computers, these days, are by and large considered computers which execute programs. Perhaps in the 90s-00s that wasn't the case since physicists cared more then about the construction of a laboratory apparatus and less about turning it into a programmable device with program and data I/O. I can't comment on what you know or don't know, but what you're writing is misleading and not accurate. The two points you've made (about what's considered computing and how modern quantum computers work) are what I refute.
- westurner 5y ago
  "Quantum computing: A taxonomy, systematic review and future" (2022) https://doi.org/10.1002/spe.3039 https://doi.org/10.1002/spe.3039 "Multi-qubit quantum logic operations with ion-implanted donor spins in silicon" (2022) https://scholar.google.com/citations?view_op=view_citation&hl=en&user=_G8qcyEAAAAJ&sortby=pubdate&citation_for_view=_G8qcyEAAAAJ:FPJr55Dyh1AC https://scholar.google.com/citations?view_op=view_citation&h... https://meetings.aps.org/Meeting/MAR22/Session/G39.1 https://meetings.aps.org/Meeting/MAR22/Session/G39.1 (Veritasium video) > Among semiconductor qubits, the electron and nuclear spins of donors in silicon play a special role for their conceptual simplicity (a 31P donor in silicon is similar to hydrogen in vacuum) and their exceptional coherence times [1] and 1-qubit gate fidelities [2]. Here I will present experimental progress on multi-qubit logic operations with donor spins, which point to several credible pathways for scalability using ion-implanted donors in MOS-compatible devices. The current state of the art is a hybrid electron-nuclear 3-qubit processor [3], where two 31P nuclear spin qubits are coupled to the same electron. The shared electron enables a geometric nuclear two-qubit CZ gate, which we perform with 99.37% average fidelity. NMR single-qubit gates reach fidelities up to 99.95%, and state preparation and measurement are performed with 98.95% fidelity. These three metrics show how close this system is to operating at fault-tolerance thresholds. Further, we entangle the two nuclei with the electron to prepare a 3-qubit GHZ state with 92.5% fidelity. Electron-nuclear entanglement unlocks the ability to connect nuclear qubits via the electrons, for instance using exchange interactions [4]. We have operated a weakly (~10 MHz) exchange-coupled 31P donor pair as a 2-qubit electron system, with native CROT gates performed by resonant microwaves. Gate fidelity benchmarks are underway and will be reported at the Meeting. On the engineering side, we have demonstrated the ability to implant single donors in silicon with confidence up to 99.85% [5]. This striking result identifies ion implantation as a scalable and accurate manufacturing strategy for spin-based quantum computers in silicon. QoS: Quantum-on-Silicon The survey article above just says "[Quantum] Output"? Is that different from registers? How long are those states ah coherent? "Researchers store a quantum bit for a record-breaking 20 milliseconds" (2022) https://phys.org/news/2022-03-quantum-bit-fora-record-breaking-milliseconds.html https://phys.org/news/2022-03-quantum-bit-fora-record-breaki... > By managing to store a qubit in a crystal (a "memory") for 20 milliseconds, a team from the University of Geneva (UNIGE) has set a world record and taken a major step towards the development of long-distance quantum telecommunications networks. What are repeaters, and what are [quantum] prepared states in re: registers and longer-term storage for non-collapsed (or just probabilistic?) qubit outputs?