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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

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
I don't understand your point. Everything I said above is completely and totally technically correct from a physical point of view. You are ascribing to my statements meaning which I did not intend. Modern trapped ion computers are doing the same underlying operations as NMR: you are using RF or other energy to perturb the energy states of underlying particles or other components, and reading out the results. There was also a whole field called 'dna computing' which you would call biologists in a lab, but they were absolutely doing computing
- reikonomusha 5y ago
  I'm intently curious what sort of common-sense explanation you'd ascribe to how one programs an ordinary classical computer. Would you describe a computer programmer as one who orchestrates a delicate movement of charge through an intricate arrangement of n–p–n bipolar transistors? Quantum computers really can be instructed to do an abstract operation on an abstract quantity, just like I can on an ordinary computer. You tell quantum computers to add and multiply, just as you do in your favorite programming language. In the programming language Quil, which a couple quantum computers of different base technologies use, one can literally write down a matrix of numbers in a program to define a new mathematical function, and later use that function to manipulate the contents of the computer's RAM[1]. On top of this, you can have loops, boolean conditions, and all that jazz a programmer expects. You don't even need a physicist to do this; a completely physics-ignorant programmer could do this. All this business about energy levels, evolution, etc. are distractions, just as the electrodynamics of a transistor are distractions from what it means to program a computer. [1] I'm abusing the word "RAM" here, where I truly mean the state of your quantum register(s).
  - westurner 5y ago
    > one can literally write down a matrix of numbers in a program to define a new mathematical function, and later use that function to manipulate the contents of the computer's RAM[1]. This "Quantum Computing for Computer Scientists" video https://youtu.be/F_Riqjdh2oM https://youtu.be/F_Riqjdh2oM explains classical and quantum operators as just matrices. What are other good references? Quantum state: https://en.wikipedia.org/wiki/Quantum_state https://en.wikipedia.org/wiki/Quantum_state Quantum logic; quantum logical operators: https://en.wikipedia.org/wiki/Quantum_logic https://en.wikipedia.org/wiki/Quantum_logic > All this business about energy levels, evolution, etc. are distractions, just as the electrodynamics of a transistor are distractions from what it means to program a computer. But a classical simulator - like e.g. qiskit - for a quantum circuit/experiment/function must run the experiment very^very^very many times to even probabilistically approximate a sufficient quantum system; because of the combinatorial probabilistic explosion that results from adding just one more basis state. What are the fundamental limitations of quantum simulators? Maybe it's possible. Quantum simulator: https://en.wikipedia.org/wiki/Quantum_simulator https://en.wikipedia.org/wiki/Quantum_simulator - [ ] Maybe Twistor theory has insight into a classical geometrical formulation that could be run on a non-QC? Amplituhedron: https://en.wikipedia.org/wiki/Amplituhedron https://en.wikipedia.org/wiki/Amplituhedron [Photon] wave-particle constructive superpositions approximate which operators, which may form a neat topology like this: - [ ] > A research question for a new school year: > The classical logical operators form a neat topology. Should we expect there to be such symmetry and structure amongst the quantum operators as well? https://commons.m.wikimedia.org/wiki/File:Logical_connectives_Hasse_diagram.svg https://commons.m.wikimedia.org/wiki/File:Logical_connective...

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

I don't understand your point. Everything I said above is completely and totally technically correct from a physical point of view. You are ascribing to my statements meaning which I did not intend. Modern trapped ion computers are doing the same underlying operations as NMR: you are using RF or other energy to perturb the energy states of underlying particles or other components, and reading out the results. There was also a whole field called 'dna computing' which you would call biologists in a lab, but they were absolutely doing computing

reikonomusha 5y ago
I'm intently curious what sort of common-sense explanation you'd ascribe to how one programs an ordinary classical computer. Would you describe a computer programmer as one who orchestrates a delicate movement of charge through an intricate arrangement of n–p–n bipolar transistors? Quantum computers really can be instructed to do an abstract operation on an abstract quantity, just like I can on an ordinary computer. You tell quantum computers to add and multiply, just as you do in your favorite programming language. In the programming language Quil, which a couple quantum computers of different base technologies use, one can literally write down a matrix of numbers in a program to define a new mathematical function, and later use that function to manipulate the contents of the computer's RAM[1]. On top of this, you can have loops, boolean conditions, and all that jazz a programmer expects. You don't even need a physicist to do this; a completely physics-ignorant programmer could do this. All this business about energy levels, evolution, etc. are distractions, just as the electrodynamics of a transistor are distractions from what it means to program a computer. [1] I'm abusing the word "RAM" here, where I truly mean the state of your quantum register(s).
- westurner 5y ago
  > one can literally write down a matrix of numbers in a program to define a new mathematical function, and later use that function to manipulate the contents of the computer's RAM[1]. This "Quantum Computing for Computer Scientists" video https://youtu.be/F_Riqjdh2oM https://youtu.be/F_Riqjdh2oM explains classical and quantum operators as just matrices. What are other good references? Quantum state: https://en.wikipedia.org/wiki/Quantum_state https://en.wikipedia.org/wiki/Quantum_state Quantum logic; quantum logical operators: https://en.wikipedia.org/wiki/Quantum_logic https://en.wikipedia.org/wiki/Quantum_logic > All this business about energy levels, evolution, etc. are distractions, just as the electrodynamics of a transistor are distractions from what it means to program a computer. But a classical simulator - like e.g. qiskit - for a quantum circuit/experiment/function must run the experiment very^very^very many times to even probabilistically approximate a sufficient quantum system; because of the combinatorial probabilistic explosion that results from adding just one more basis state. What are the fundamental limitations of quantum simulators? Maybe it's possible. Quantum simulator: https://en.wikipedia.org/wiki/Quantum_simulator https://en.wikipedia.org/wiki/Quantum_simulator - [ ] Maybe Twistor theory has insight into a classical geometrical formulation that could be run on a non-QC? Amplituhedron: https://en.wikipedia.org/wiki/Amplituhedron https://en.wikipedia.org/wiki/Amplituhedron [Photon] wave-particle constructive superpositions approximate which operators, which may form a neat topology like this: - [ ] > A research question for a new school year: > The classical logical operators form a neat topology. Should we expect there to be such symmetry and structure amongst the quantum operators as well? https://commons.m.wikimedia.org/wiki/File:Logical_connectives_Hasse_diagram.svg https://commons.m.wikimedia.org/wiki/File:Logical_connective...