Dynamical decoupling of wells for an energy gap protected qubit
Selective frequency dissipation is implemented that enables cooling of energy gap protected qubits such that excited energy states resulting from heating or other undesired processes are returned to a lower excited energy state or a ground state manifold, thus reducing the probability of errors. Also, the selective frequency dissipation inhibits leakage from the energy gap protected qubits when in the ground state. Additionally or alternatively, Hamiltonian engineering by inducing parity rotations is implemented to decouple the wells of the energy gap protected qubit to further reduce errors when leakage does happen.
1 . A system comprising:
quantum hardware configured to:
prepare protected ground states of an energy gap protected qubit;
stabilize the ground states of a ground state manifold of a Hamiltonian for the energy gap protected qubit; and
undergo pulse sequences inducing rotations or oscillations to suppress tunneling between non-protected excited states of an oscillator mode used to encode the energy gap protected qubit,
wherein the pulse sequences reduce a probability of a bit-flip error occurring in the energy gap protected qubit.
2 . The system of claim 1 further comprising:
a drive, wherein:
the pulse sequences are applied via the drive; and
the drive is a pulsed drive.
3 . The system of claim 1 further comprising:
a drive, wherein:
the pulse sequences are applied via the drive; and
the drive is a continuous pulsed drive.
4 . The system of claim 1 further comprising:
a drive, wherein:
the pulse sequences are applied via the drive; and
the drive is configured to reduce the probability of the bit-flip error occurring in the energy gap protected qubit.
5 . The system of claim 1 , wherein the quantum hardware is further configured to implement a resonator, wherein:
the resonator comprises the energy gap protected qubit and a drive; and
the pulse sequences are applied via the drive.
6 . The system of claim 1 , wherein the quantum hardware is further configured to implement:
a decay channel, wherein:
dissipation is permitted from the energy gap protected qubit via the decay channel at frequencies at which the system moves from a higher excited energy state of the non-protected excited states to a lower energy state, wherein the lower energy state is the ground state manifold or an intermediate excited energy state of the non-protected excited states; and
emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the ground state manifold.
7 . The system of claim 1 , wherein the energy gap protected qubit is a Kerr cat qubit.
8 . The system of claim 7 , wherein the pulse sequences inducing rotations are pulse sequences inducing parity or Z rotations.
9 . The system of claim 1 , wherein the energy gap protected qubit is configured to encode more than two levels of quantum information.
10 . A method of stabilizing an energy gap protected qubit, the method comprising:
preparing protected ground states of an energy gap protected qubit;
stabilizing the ground states of a ground state manifold of a Hamiltonian for the energy gap protected qubit; and
applying a drive that induces rotations or oscillations to suppress tunneling between non-protected excited states of a mode used to encode the energy gap protected qubit,
wherein the drive is configured to reduce a probability of a bit-flip error occurring in the energy gap protected qubit.
11 . The method of claim 10 , wherein the drive suppresses tunneling via targeting one or more reductions of effective tunneling coefficients (χ n ) in the Hamiltonian defined for the energy gap protected qubit.
12 . The method of claim 10 , wherein the drive is a continuous drive configured to reduce the probability of the bit-flip error occurring in the energy gap protected qubit.
13 . The method of claim 10 , wherein the energy gap protected qubit is a cat qubit.
14 . The method of claim 10 , wherein the energy gap protected qubit is a Kerr cat qubit.
15 . The method of claim 10 , wherein the drive is a pulsed drive configured to reduce the probability of the bit-flip error occurring in the energy gap protected qubit.
16 . The method of claim 10 , further comprising:
dissipating photons via a decay channel, wherein:
dissipation is permitted from the energy gap protected qubit via the decay channel at frequencies at which the oscillator mode moves from a higher excited energy state of the non-protected excited states to a lower energy state, wherein the lower energy state is the ground state manifold or an intermediate excited energy state of the non-protected excited states; and
emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the ground state manifold.
17 . One or more non-transitory, computer-readable, storage media storing program instructions, that when executed cause:
preparation of protected ground states of an energy gap protected qubit;
stabilization of the ground states of a ground state manifold of a Hamiltonian for the energy gap protected qubit; and
application of a drive that induces rotations or oscillations to suppress tunneling between non-protected excited states of a mode used to encode the energy gap protected qubit
wherein the drive is configured to reduce a probability of a bit-flip error occurring in the energy gap protected qubit.
18 . The one or more non-transitory, computer-readable, storage media of claim 17 , wherein the program instructions, when executed on or across one or more processors, cause the one or more processors to:
configure the drive as a continuous drive that reduces the probability of the bit-flip error occurring in the energy gap protected qubit.
19 . The one or more non-transitory, computer-readable, storage media of claim 17 , wherein the program instructions, when executed on or across one or more processors, cause the one or more processors to:
configure the drive as a pulsed drive that emits pulse sequences such that the pulse sequences suppress leakage out of a code space defined by the energy gap protected qubit.
20 . The one or more non-transitory, computer-readable, storage media of claim 17 , wherein the program instructions, when executed on or across the one or more processors, further cause the one or more processors to:
dissipate photons via a decay channel, wherein:
dissipation is permitted from the energy gap protected qubit via the decay channel at frequencies at which the oscillator mode moves from a higher excited energy state of the non-protected excited states to a lower energy state, wherein the lower energy state is the ground state manifold or an intermediate excited energy state of the non-protected excited states; and
emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the ground state manifold.