# US 2023/0053543 A1 · Driving dark modes to facilitate entanglement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2023/0053543 A1 - Document ID: US20230053543A1 - Status: Published application - Kind: A1 - Application number: 17/409,425 - Filed: 2021-08-23 - Published: 2023-02-23 - Earliest claimed: 2021-08-23 - Assignees: International Business Machines Corporation - Applicants: International Business Machines Corporation - Inventors: Aaron Finck; John Blair; April Carniol - Web page: https://patentgrep.com/patent/US20230053543A1 ## 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 - H03K 3/38: by the use, as active elements, of superconductive devices - G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) ## Abstract Systems and techniques that facilitate entanglement via driving dark modes are provided. In various embodiments, a method can comprise accessing a first multi-mode qubit and a second multi-mode qubit. In various cases, the first multi-mode qubit can be coupled to the second multi-mode qubit by a mode-selective coupler. In various aspects, the method can further comprise exciting a dark mode of the first multi-mode qubit. In various cases, the exciting the dark mode can entangle the first multi-mode qubit with the second multi-mode qubit. ## Claims ### Claim 1 A method, comprising: accessing a first multi-mode qubit that is coupled by a mode-selective coupler to a second multi-mode qubit; and exciting a dark mode of the first multi-mode qubit, wherein the exciting the dark mode entangles the first multi-mode qubit with the second multi-mode qubit. ### Claim 2 (depends on 1) The method of claim 1, wherein the exciting the dark mode of the first multi-mode qubit comprises: applying a pi-pulse to the first multi-mode qubit. ### Claim 3 (depends on 2) The method of claim 2, wherein the exciting the dark mode of the first multi-mode qubit further comprises: idling for a predetermined time period after the applying the pi-pulse; and applying a negative pi-pulse to the first multi-mode qubit based on the predetermined time period elapsing. ### Claim 4 (depends on 3) The method of claim 3, wherein the mode-selective coupler couples the dark mode of the first multi-mode qubit to another dark mode of the second multi-mode qubit, and wherein the mode-selective coupler leaves a bright mode of the first multi-mode qubit uncoupled from another bright mode of the second multi-mode qubit. ### Claim 5 (depends on 4) The method of claim 4, wherein the first multi-mode qubit and the second multi-mode qubit are two-junction transmon qubits. ### Claim 6 (depends on 5) The method of claim 5, wherein the mode-selective coupler is a capacitor that directly couples a middle capacitor pad of the first multi-mode qubit to another middle capacitor pad of the second multi-mode qubit. ### Claim 7 (depends on 5) The method of claim 5, wherein the mode-selective coupler is a bus resonator that capacitively couples a middle capacitor pad of the first multi-mode qubit to another middle capacitor pad of the second multi-mode qubit. ### Claim 8 (depends on 3) The method of claim 3, further comprising: applying an echo pi-pulse to a third multi-mode qubit that is coupled to the first multi-mode qubit. ### Claim 9 A device, comprising: a first multi-mode qubit and a second multi-mode qubit; and a mode-selective coupler that couples the first multi-mode qubit to the second multi-mode qubit, wherein the mode-selective coupler is configured to, upon excitation of a dark mode of the first multi-mode qubit, entangle the first multi-mode qubit with the second multi-mode qubit. ### Claim 10 (depends on 9) The device of claim 9, wherein the dark mode of the first multi-mode qubit is excited via application of a pi-pulse to the first multi-mode qubit. ### Claim 11 (depends on 10) The device of claim 10, wherein the dark mode of the first multi-mode qubit is de-excited via application of a negative pi-pulse to the first multi-mode qubit, and wherein the negative pi-pulse is applied after a predetermined time period has elapsed following the application of the pi-pulse. ### Claim 12 (depends on 11) The device of claim 11, wherein the mode-selective coupler couples the dark mode of the first multi-mode qubit to another dark mode of the second multi-mode qubit, and wherein the mode-selective coupler leaves a bright mode of the first multi-mode qubit uncoupled from another bright mode of the second multi-mode qubit. ### Claim 13 (depends on 12) The device of claim 12, wherein the first multi-mode qubit and the second multi-mode qubit are two-junction transmon qubits. ### Claim 14 (depends on 13) The device of claim 13, wherein the mode-selective coupler is a capacitor that directly couples a middle capacitor pad of the first multi-mode qubit to another middle capacitor pad of the second multi-mode qubit. ### Claim 15 (depends on 13) The device of claim 13, wherein the mode-selective coupler is a bus resonator that capacitively couples a middle capacitor pad of the first multi-mode qubit to another middle capacitor pad of the second multi-mode qubit. ### Claim 16 (depends on 11) The device of claim 11, further comprising: a third multi-mode qubit that is coupled to the first multi-mode qubit, wherein an echo pi-pulse is applied to the third multi-mode qubit. ### Claim 17 A method, comprising: accessing a first two-junction transmon qubit and a second two-junction transmon qubit, wherein a middle capacitor pad of the first two-junction transmon qubit is capacitively coupled to another middle capacitor pad of the second two-junction transmon qubit; and entangling the first two-junction transmon qubit with the second two-junction transmon qubit, by driving the first two-junction transmon qubit with a dark mode excitation pulse sequence. ### Claim 18 (depends on 17) The method of claim 17, wherein the middle capacitor pad of the first two-junction transmon qubit being capacitively coupled to the another middle capacitor pad of the second two-junction transmon qubit causes the dark mode of the first two-junction transmon qubit to be coupled to another dark mode of the second two-junction transmon qubit, and wherein the middle capacitor pad of the first two-junction transmon qubit being capacitively coupled to the another middle capacitor pad of the second two-junction transmon qubit causes a bright mode of the first two-junction transmon qubit to remain uncoupled from another bright mode of the second two-junction transmon qubit. ### Claim 19 (depends on 17) The method of claim 17, wherein the dark mode excitation pulse sequence includes a first pi-pulse, a first idle time, and a first negative pi-pulse. ### Claim 20 (depends on 19) The method of claim 19, wherein the dark mode excitation pulse sequence further includes a second pi-pulse, a second idle time, and a second negative pi-pulse, wherein the first negative pi-pulse and the second pi-pulse are separated by an echo pi-pulse applied to a third two-junction transmon qubit that is coupled to the first two-junction transmon qubit.