| CPC G06N 10/40 (2022.01) | 8 Claims |
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1. A quantum computing system comprising:
a quantum subsystem drivable to host a bosonic cat state having N coherent states wherein N is a prime number greater than two, the N coherent states defining a computational space;
driving hardware operably connected to drive the quantum subsystem to host the bosonic cat state, said driving further comprising controlling a number of bosons in the quantum subsystem; and
a controller operably connected to control the driving hardware in accordance with control instructions,
wherein the control instructions include a function to generate via said controller an initial state of the bosonic cat state defined as a given superposition of two distinct logical states representing logical information, the two distinct logical states spanning a logical subspace within the computational space; and
wherein said initial state of the bosonic cat state is generated so that phase shifting from the initial state stemming from any number of boson losses in the quantum subsystem occurring outside of said controlling the number of bosons is constrained to either lead:
i) to a modified state which lies outside the logical subspace while preserving said logical information, or
ii) back to the initial state; and
wherein the N coherent states are representable as points around a circle in a phase space of the quantum subsystem, and wherein the logical states are rotationally asymmetric in said phase space when the bosonic cat state is rotated around a circle in the phase space due to said any number of boson losses;
wherein a rotational symmetry is broken by attributing a coefficient of zero to at least one of the coherent states;
wherein N=3;
wherein the quantum subsystem is drivable to host coherent states |a>, ae2πi/3>, |ae−2πi/3>, wherein a first one of the logical states is encoded as a first one of the coherent states, a second one of the logical states is encoded in a combination of the two other coherent states;
wherein said bosons are photons, and wherein:
the quantum subsystem is a superconducting circuit comprising a resonator having a resonator frequency;
the driving hardware includes a three-photon drive having a drive frequency; and
the bosonic cat state is driven by the driving hardware based on the Hamiltonian HNEW=−Kâ†2â2+ε3(â†3+â3)+Δâ†â where K is an amplitude of a Kerr nonlinearity, ε3 is an amplitude of the three-photon drive, and A is a detuning between the drive frequency and the resonator frequency; and
wherein the controller is further configured to control the driving hardware such that |ε3|Δ|, and ε3 (â†3+â†3)<<Δâ†â.
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