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Quantum Computing Hardware

Which correctly describes a neutral-atom quantum computer?

  1. AMany atoms are arranged and held with optical tweezers (focused laser beams), and two-qubit gates use the strong interaction that arises when atoms are excited to Rydberg states
  2. BAtoms are embedded in a silicon crystal, and the charge of their nuclei is read out with electrodes
  3. CAtoms have no charge, so they do not interact at all and two-qubit gates are impossible
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Answer: A. Many atoms are arranged and held with optical tweezers (focused laser beams), and two-qubit gates use the strong interaction that arises when atoms are excited to Rydberg states

In a neutral-atom system, laser-cooled atoms such as rubidium are caught one by one in a vacuum with focused laser beams (optical tweezers) and arranged in two-dimensional or other arrays. Two energy levels of each atom serve as a qubit, and two-qubit gates use the strong interaction that appears when atoms are excited to Rydberg states, in which an electron occupies a very large orbit. The optical tweezers can move and rearrange the atoms, so a strength of this approach is the flexibility to connect many qubits. On the other hand, loss of trapped atoms and the time needed for measurement and rearrangement are challenges.

  • A. Correct. The atoms are arranged with optical tweezers, and gates use the Rydberg interaction.
  • B. Embedding atoms such as phosphorus in silicon is one type of silicon spin qubit, which mainly uses electron or nuclear spins.
  • C. The interaction is weak in the normal state, but excitation to Rydberg states produces a strong interaction, which is used for two-qubit gates.
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More Quantum Computing Hardware questions

  1. What is the main reason silicon spin qubits are expected to suit large-scale systems?
  2. Why is silicon enriched in the isotope ²⁸Si (isotopically purified silicon) used for silicon spin qubits?
  3. Which correctly describes photonic quantum computing, which uses photons as qubits?
  4. A rotated surface code of code distance d uses, for one logical qubit, d² physical data qubits and d² − 1 physical measurement qubits that check for errors. For d = 15, how many physical qubits does one logical qubit need?
  5. Suppose the logical error rate p_L of a surface code can be approximated as p_L ∝ (p/p_th)^((d+1)/2), using the physical error rate p, the threshold p_th and the code distance d. With p = 0.1% and p_th = 1%, which is closest to the ratio of logical error rates when d is increased from 5 to 9 (the value at d = 5 divided by the value at d = 9)?