# US 2021/0278745 A1 · Quantum wavelength converter between a microwave signal and an optical signal

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- Number: US 2021/0278745 A1
- Document ID: US20210278745A1
- Status: Published application
- Kind: A1
- Application number: 17/314,224
- Filed: 2021-05-07
- Published: 2021-09-09
- Earliest claimed: 2018-11-07
- Assignees: Qphox B.V.
- Applicants: QphoX B.V.
- Inventors: Simon GROEBLACHER; Moritz FORSCH; Robert Hugh James STOCKILL
- Web page: https://patentgrep.com/patent/US20210278745A1

## CPC

- G02F 2/02: Frequency-changing of light, e.g. by quantum counters
- G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
- G06E 3/005: {using electro-optical or opto-electronic means}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
- G06E: OPTICAL COMPUTING DEVICES (digital storage using optical elements G11C13/04)

## Abstract

The present invention is in the field of a quantum wavelength converter between a microwave signal and an optical signal and vice versa. In the converter a nanoscale cavity optomechanical circuit is used in which optomechanical cavities supporting colocalized infrared photons and microwave phonons are combined with a photonic and a phononic waveguide.

## Claims

### Claim 1

A quantum transduction system including a cryogenically cooled piezoelectric, resonant electro-mechanical interface coupling device.

### Claim 2 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is configured to be resonant with incoming microwave photons.

### Claim 3 (depends on 2)

The quantum transduction system of claim 2 in which the piezoelectric coupling device has a gigahertz frequency mechanical mode.

### Claim 4 (depends on 3)

The quantum transduction system of claim 3 in which the piezoelectric coupling device has a gigahertz frequency mechanical mode centered at 2.7 GHz.

### Claim 5 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is configured to receive an input quantum state in the microwave domain, and to generate a phonon state that encodes the input quantum state information and, through a quantum coherent state conversion process, couples that quantum state information to an optical quantum state which it then outputs at an optical (UV, VIS, or IR) wavelength.

### Claim 6 (depends on 5)

The quantum transduction system of claim 5 in which the optical quantum state that is created from the phonon state through the conversion process is evanescently coupled to an optical waveguide that is then coupled to an optical fiber.

### Claim 7 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is configured to generate on average a single phonon for each incoming photon.

### Claim 8 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is configured to operate at a single phonon level.

### Claim 9 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is configured to receive an optical quantum state that encodes quantum information, and through a coherent state conversion process, to couple that quantum state information to a phonon state that encodes the quantum state information and convert that phonon state to a microwave signal that encodes the quantum state information.

### Claim 10 (depends on 9)

The quantum transduction system of claim 9 in which the optical quantum state is evanescently coupled to an optical waveguide.

### Claim 11 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device comprises a resonant electro-mechanical interface that is coupled to an opto-mechanical resonance interface.

### Claim 12 (depends on 11)

The quantum transduction system of claim 11 in which the resonant electro-mechanical interface is configured to generate a phonon state that encodes input quantum state information and, through a quantum coherent state conversion process, the opto-mechanical resonance interface is configured to couple that quantum state information to an optical quantum state.

### Claim 13 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is a heterogenous structure integrated into a chip and comprises an electro-mechanical resonator that is mechanically coupled to an opto-mechanical resonator, and different materials are used for the electro-mechanical resonator and for the optical opto-mechanical resonator.

### Claim 14 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is a homogenous structure integrated into a chip and comprises an electro-mechanical resonator that is mechanically coupled to an opto-mechanical resonator, and the same material is used for the electro-mechanical resonator and for the opto-mechanical resonator.

### Claim 15 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device includes a photon absorption surface layer to inhibit absorption of photons that would otherwise heat the mechanical resonance coupling device and hence add unwanted noise.

### Claim 16 (depends on 15)

The quantum transduction system of claim 15 in which the piezoelectric coupling device operates at optical (UV, VIS, or IR) wavelengths and the photon absorption layer does not absorb light in those wavelengths.

### Claim 17 (depends on 16)

The quantum transduction system of claim 16 in which the photon absorption surface layer is selected from a dielectric material, wherein a cation of the dielectric material is selected from Al, Ti, Ta, and Si, and wherein the anion of the dielectric material is selected from O, N, and C, and combinations thereof.

### Claim 18 (depends on 16)

The quantum transduction system of claim 16 in which the light absorption layer is a conformal layer, and the light absorption inhibiting layer has a thickness of 1-10 nm, preferably 2-8 nm, such as 4-6 nm.

### Claim 19 (depends on 16)

The quantum transduction system of claim 16 in which the light absorption layer is at least one of an ALD layer, and a chemically oxidized layer.

### Claim 20 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device includes materials selected from the following materials: III/V materials, wherein “III” materials are selected from B, Al, Ga, In, and Tl, and wherein “V” materials are selected from N, P, As, and Sb, such as GaN, GaP, AlN, and AlP, and niobates, tantalates, and vanadates, such as monovalent salts thereof, such as Li comprising salts thereof, such as LiNbO3, and LiTaO3.

### Claim 21 (depends on 11)

The quantum transduction system of claim 11 in which the material of the opto-mechanical resonance interface is selected from III/V materials, such as GaAs, and LiNb03, and LiTaO3, a dielectric material, such as silicon oxide, such as quartz, silicon nitride, and silicon carbide, and silicon.

### Claim 22 (depends on 1)

The quantum transduction system of claim 1 in which the piezoelectric coupling device is at least in part integrated onto a single chip.

### Claim 23 (depends on 11)

The quantum transduction system of claim 11 in which the resonant electro-mechanical interface is a 1D piezoelectric optomechanical crystal (OMC) mechanically coupled to an interdigital transducer (IDT).

### Claim 24 (depends on 11)

The quantum transduction system of claim 11 in which the resonant electro-mechanical interface is a piezoelectric optomechanical crystal with a gigahertz frequency mechanical mode.

### Claim 25 (depends on 23)

The quantum transduction system of claim 23 in which the piezoelectric optomechanical crystal is configured to be cooled to its quantum ground state and to remain in the ground state during conversion of a microwave quantum state to an optical quantum state.

### Claim 26 (depends on 24)

The quantum transduction system of claim 24 in which the piezoelectric optomechanical crystal is configured to generate a single phonon from a single input photon.

### Claim 27 (depends on 11)

The quantum transduction system of claim 11 in which the resonant electro-mechanical interface is configured to generate surface acoustic waves.

### Claim 28 (depends on 11)

The quantum transduction system of claim 11 in which the opto-mechanical resonance interface includes a periodic structure shaped and sized to generate optical resonance.

### Claim 29 (depends on 1)

The quantum transduction system of claim 1 in which the system includes a cryostat or cooler that encloses the mechanical resonance coupling device and the cryostat or cooler is configured to cryogenically cool the piezoelectric coupling device to an operational state selected from the following: less than 5K; less than 1K; less than 300 mK; less than 100 mK; less than 25 mK; less than 15 mK; less than 1000% of the applicable quantum ground state energy; less than 100% of the applicable quantum ground state energy; less than 50% of the applicable quantum ground state energy; less than 15% of the applicable quantum ground state energy; close to the quantum limit.

### Claim 30 (depends on 1)

The quantum transduction system of claim 1 in which the system outputs a signal at an optical telecom low-loss wavelength and is configured to couple to one or more of the following: an optical fiber; a quantum processor operating in the microwave domain with a network operating in the optical (UV, VIS, IR) domain; a network of quantum processors, each operating in the microwave domain, using a fiber optic network operating in the optical domain; a distributed quantum computing network; a quantum internet.