# US 12,001,919 B1 · Frequency selective photon dissipation for an energy gap protected qubit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,001,919 B1 - Document ID: US12001919B1 - Status: Granted - Kind: B1 - Application number: 17/364,813 - Filed: 2021-06-30 - Granted: 2024-06-04 - Earliest claimed: 2021-06-30 - Assignees: Amazon Technologies, Inc. - Applicants: Amazon Technologies, Inc. - Inventors: Harald Esko Jakob Putterman; Joseph Kramer Iverson; Liang Jiang; Fernando Brandao; Kyungjoo Noh; Oskar Jon Painter; Qian Xu - Web page: https://patentgrep.com/patent/US12001919B1 ## CPC - G06N 10/00: Quantum computing, i.e. information processing based on quantum-mechanical phenomena - G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control - G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS ## Abstract 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. ## Claims ### Claim 1 A system comprising: quantum hardware configured to implement: a mode configured to: stabilize an approximately degenerate ground state of a Hamiltonian in an oscillator mode for an energy gap protected qubit; and a decay channel for the mode, 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 to a lower energy state, wherein the lower energy state is a degenerate ground state manifold or an intermediate excited energy state; and emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the degenerate ground state manifold. ### Claim 2 (depends on 1) The system of claim 1, wherein the decay channel comprises: a plurality of filter modes, wherein a first one of the filter modes is coupled to the energy gap protected qubit and another one of the filter modes is coupled to a bath configured to absorb an excitation or excitations dissipated from the energy gap protected qubit via the plurality of filter modes, wherein one or more of: frequencies of the filter modes, a coupling between the first filter mode and the energy gap protected qubit, one or more respective couplings between the filter modes, or a coupling between the other filter mode and the bath, are selected such that: dissipation is permitted from the energy gap protected qubit via the filter modes at frequencies at which the system moves from a higher excited energy state to a lower energy state, wherein the lower energy state is a degenerate ground state manifold or an intermediate excited energy state; and emission of photons is restricted from the energy gap protected qubit via the filter modes at the frequency of the degenerate ground state manifold. ### Claim 3 (depends on 2) The system of claim 2, wherein the filter modes and the bath are configured to implement frequency selective photon loss for the energy gap protected qubit. ### Claim 4 (depends on 1) The system of claim 1, wherein the energy gap protected qubit is a Kerr qubit. ### Claim 5 (depends on 1) The system of claim 1, wherein the energy gap protected qubit is a cat qubit. ### Claim 6 (depends on 1) The system of claim 1, wherein the energy gap protected qubit is a Kerr-cat qubit stabilized using a Kerr nonlinearity of a drive of a resonator and a two photon drive. ### Claim 7 (depends on 1) The system of claim 1, wherein the dissipation is a single photon dissipation. ### Claim 8 (depends on 2) The system of claim 2, wherein: the energy gap protected qubit is a Kerr-cat qubit; the dissipation is a single photon dissipation; and the filter modes and the bath are configured to implement frequency selective single-photon loss from the Kerr-cat qubit. ### Claim 9 (depends on 8) The system of claim 8, wherein the frequency selective single photon loss mitigates heating of the Kerr-cat qubit such that excitement caused by the heating is mitigated by dissipating a photon from the Kerr-cat qubit via the filter modes such that energy states for the Kerr-cat qubit are returned to the degenerate ground state manifold. ### Claim 10 (depends on 1) The system of claim 1, further comprising a control system configured to implement active coupling of the first filter mode to the energy gap protected qubit. ### Claim 11 (depends on 10) The system of claim 10, wherein the control system is configured to turn “on” and turn “off” frequency selective photon loss from the energy gap protected qubit via the active coupling. ### Claim 12 (depends on 10) The system of claim 10, wherein the dissipation is two-photon dissipation. ### Claim 13 (depends on 1) The system of claim 1, wherein the energy gap protected qubit is a Kerr-cat qubit stabilized using a Kerr nonlinearity of a drive of a resonator, and wherein the resonator is a photonic resonator or a microwave resonator. ### Claim 14 (depends on 1) The system of claim 1, wherein the dissipation to the degenerate ground state manifold reduces a probability of occurrence of bit-flip errors. ### Claim 15 (depends on 1) The system of claim 1, wherein the restriction of emission of photons from the degenerate ground state manifold reduces a probability of occurrence of phase flip errors. ### Claim 16 (depends on 2) The system of claim 2, wherein the plurality of filter modes collectively implement a bandpass filter for dissipation from the energy gap protected qubit such that dissipation at frequencies within the band pass are permitted and dissipation at frequencies outside of the band pass are suppressed. ### Claim 17 (depends on 2) The system of claim 2, wherein the plurality of filter modes collectively implement a low pass filter for dissipation from the energy gap protected qubit such that dissipation at frequencies below a given frequency are permitted and dissipation at frequencies above the given frequency are suppressed. ### Claim 18 (depends on 1) The system of claim 1, wherein the control circuit is further configured to: undergo pulse sequences inducing Z rotations or parity oscillations to suppress tunneling between wells of the oscillator mode, wherein the respective wells correspond to the respective cat states of the energy gap protected qubit. ### Claim 19 A method comprising: stabilizing an approximately degenerate ground state of a Hamiltonian in an oscillator mode for an energy gap protected qubit; and dissipating photons from the energy gap protected qubit via a decay channel, wherein dissipation is permitted from the energy gap protected qubit via the decay channel at frequencies at which the energy gap protected qubit moves from a higher excited energy state to a lower energy state, wherein the lower energy state is a degenerate ground state manifold or an intermediate excited energy state; and emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the degenerate ground state manifold. ### Claim 20 One or more non-transitory computer-readable media storing program instructions, usable to cause a piece of quantum hardware to implement: a mode configured to: stabilize an approximately degenerate ground state of a Hamiltonian in an oscillator mode for an energy gap protected qubit; and a decay channel for the mode, 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 to a lower energy state, wherein the lower energy state is a degenerate ground state manifold or an intermediate excited energy state; and emission of photons is restricted from the energy gap protected qubit via the decay channel at a frequency of the degenerate ground state manifold.