Classifications

• • G—PHYSICS
  • G02—OPTICS
  • 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
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
• • G—PHYSICS
  • G02—OPTICS
  • 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
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/0128—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on electro-mechanical, magneto-mechanical, elasto-optic effects
  • G02F1/0131—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on electro-mechanical, magneto-mechanical, elasto-optic effects based on photo-elastic effects, e.g. mechanically induced birefringence
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/70—Photonic quantum communication
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• • G—PHYSICS
  • G02—OPTICS
  • 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
  • G02F2203/00—Function characteristic
  • G02F2203/15—Function characteristic involving resonance effects, e.g. resonantly enhanced interaction

Definitions

• the present invention relates to the field of quantum coupled systems and in particular, discloses a form of coupling of spatially separated qubits.
• a quantum internet where widely separated quantum devices are coherently connected, is a desirable requirement for local and global quantum information networks [1-3].
• Superconducting quantum devices have developed rapidly and can perform sophisticated manipulations on qubits and microwave photons locally on chip.
• Developing a quantum internet device using interconnected superconducting devices requires an important element: a device that coherently inter-converts microwave quantum information into optical quantum information, and back again - to effect a coherent optical bus between distant superconducting circuits.
• Previous proposals to interconvert electromagnetic radiation at different frequencies suggest utilising optomechanical quantum systems [4-12], atomic [13], electro-optic [14-16], and solid-state electronic ensembles [17-21].
• United States Patent 7,889,992 to DiVincenzo et al discloses one form of superconductor-optical hybrid repeater, interconnecting superconducting qubits, utilising a nonlinear tunnel junction. The operational characteristics of such a device are unknown.
• a quantum state transfer device including: a first magnetic state sensor adapted to sense the quantum state of a magnetic flux qubit; and a magnetic state to optical state transfer system, interconnected to the first magnetic state sensor and adapted to transfer the quantum state of the magnetic flux qubit to a corresponding optical quantum state in an output optical signal.
• the magnetic state to optical state transfer system includes a magnetically controlled optical modulator which modulates an optical signal in accordance with a corresponding magnetic signal so as to produce said output optical signal.
• the magnetic state to optical state transfer system includes an inductive coupling system.
• the inductive coupling system includes at least one permanent magnet.
• the inductive coupling system includes two or more inductors.
• the magnetically controlled optical modulator includes an optical cavity in which said output optical signal is modulated.
• the optical cavity can comprise a Fabry Perot cavity having dimensions modulated by a magnetically sensitive material.
• the first magnetic state sensor can comprise a magnetostrictive material.
• the optical cavity dimensions are preferably modulated by a magnetostrictive material.
• the magnetic flux qubit can comprise a superconducting qubit.
• a quantum state transfer device including: an optical cavity modulating an optical input signal, including a first mirror surface for reflection of the optical input signal and a second semi mirrored partially transparent surface for forming an optical input output signal interface; and a magnetically inductive material mechanically coupled to said first mirror surface, and further magnetically coupled to a quantum flux qubit for sensing the quantum state of the quantum flux qubit; wherein the magnetic state of the quantum flux qubit is inductively transferred to an optical quantum state of the optical input signal and output by the optical cavity device.
• a quantum state transfer device including: an optical cavity modulating an optical input signal, including a first mirror surface for reflection of the optical input signal and a second semi mirrored partially transparent surface for forming an optical input output signal interface; and a magnetostrictive material mechanically coupled to the first mirror surface, and further magnetically coupled to a quantum flux qubit for sensing the quantum state of the quantum flux qubit; wherein the magnetic state of the quantum flux qubit is transferred to an optical quantum state of the optical input signal and output by the optical cavity device.
• a method of transfer of a magnetic flux qubit quantum state to a corresponding optical quantum state including the steps of: (a) sensing the quantum state of the magnetic flux qubit utilising a magnetostrictive material; (b) utilising the magneto restrictive material to modulate an optical signal so as to impart the corresponding optical quantum state to the optical signal.
• the magneto restrictive material can be utilised to modulate the surface position of one surface of an optical cavity containing the optical signal to thereby impart the corresponding optical quantum state to the optical signal.
• Fig. 1 illustrates a schematic arrangement of an embodiment showing coupling between Qubit systems
• Fig. 2 illustrates a schematic of quantum network between two superconducting flux qubits
• Fig. 3 illustrates a graph of the time evolution of the Rabi oscillation between the optical resonator (OR) and the flux qubit (SQ) within a single node with small excitation of the mechanical resonator (MR);
• Fig. 4 illustrates a graph of the simulated coupling between two Qubits over an optical system
• Fig. 5 illustrates one design for one form of magnetic field to optical coupler.
• the preferred embodiment provides a magneto-optomechanical system that can interconvert microwave-to-optical quantum information.
• the preferred embodiment utilises the effective superconducting-optical coupling strength to coherently transfer quantum information between two spatially separated superconducting qubits via an optical fibre.
• the preferred embodiments make use of the magnetic field generated by the supercurrent in a flux qubit to modulate the motional and optical properties of a high-Q optical cavity and, via this, to coherently transfer quantum information between two spatially separated superconducting qubits.
• the fidelity of transfer is predicted to be as high as ⁇ 0.8 for a transmission loss of up to 10%.
• the preferred embodiment provides a quantum interface or coupler between superconducting qubits and optical photons and the utilisation of such interfaces to coherently transfer quantum information optically between spatially remote superconducting qubits.
• This coherent transfer can thus serve as the underlying architecture for a genuine quantum internet.
• An important element of the preferred embodiment is the utilisation of a magneto-mechanical interaction to provide strong coupling between the quantum state of a superconducting flux qubit (SQ) and a mechanical resonator (MR), which in turn couples via radiation pressure to an optical resonator (OR).
• SQ superconducting flux qubit
• MR mechanical resonator
• OR optical resonator
• the configuration can achieve a high fidelity coherent swap between the quantum state of the SQ and the OR in an individual node.
• By coupling two nodes via an optical fibre it is possible to create a small quantum network and a protocol to swap the SQ quantum states between the nodes.
• Fig. 1 there is provided a schematic illustration of one form of the embodiment of the invention 1.
• Each node provides an individual superconducting qubit system e.g. 2, 3, 4.
• the coupling is provided by a microwave to optical interface 6, 7 which interconnects to a corresponding optical to microwave interface 8, 9.
• the qubit system of a first node is coupled to an adjacent node's qubit system.
• further coupled nodes can be added.
• FIG. 2 there is illustrated an arrangement 20 coupling two adjacent nodes A and B.
• Node A and B are identical and each node consists of a flux qubit e.g. 21 which is magnetically coupled to a neighbouring optomechanical system 22.
• By driving the flux qubit it is possible to control the detuning of it's addressed states from the mechanical resonance.
• each node consists of an OR supporting one optical cavity mode and one mechanical vibrational mode, and a SQ.
• the optical cavity mode a in the y ' th node (j £ ⁇ A, B ⁇ ) has a resonance frequency ⁇ , and an intrinsic decay rate ⁇ ® . It couples to a nearby optical fiber 23 with a coupling K and connects with the other node via circulator 24 and the fiber 25.
• the K ex 0) denote the couplings into the waveguide connecting the two distant nodes.
• the resonance frequency and relaxation rate of mechanical motion mode S, of the y ' th OR are co m ® and y m ® respectively.
• the MR can be bonded to a magnetostrictive material like Terfenol-D, which, in the presence of a magnetic field expands and thus can be used to drive the mechanical motion.
• This kind of magnetomechanical coupling has been used for magnetic field sensing and can be quite substantial [22].
• Each SQ can be modelled as a two-level system (TLS) with the transition frequency ⁇ ⁇ 0) driven by a classical microwave field. The frequency ⁇ ⁇ 0) can be tuned via a biased magnetic field.
• the two nodes are connected by an optical fiber to form a quantum network.
• l/2 is the zero-point width of the mechanical fluctuations with effective mass m.
• H cff /h A c 'a + ; m b b 4- ⁇ Ga' + 6 * *o)(6 ⁇ + b)
• a c and ⁇ is the optical cavity damping rate (the mechanical damping is much smaller).
• the parameters A c , ⁇ and coupling G are tunable while co m , and ⁇ are not.
• L noise p describes the open system dynamics of the optomechanical resonators and flux qubits.
• the second line breaks time -reversal symmetry and models the quantum transfer from the node i to the node j or reversely, while Kj is the j th optical cavity decay rate and ⁇ / represents photon loss in the transfer (initially taking ⁇ / ⁇ 1 ) .
• 0) > while the mechanical resonator is subject to a thermal bath at a temperature T ⁇ lOmK, with n t/ , 0.2.
• the photon, mechanical mode and flux qubit interact resonantly.
• Fig. 3 illustrates a graph 30 of the time evolution of the Rabi oscillation between the optical resonator (OR) and the flux qubit (SQ) within a single node with small excitation of the mechanical resonator (MR).
• many nodes can be connected together using the optical fiber as a quantum bus.
• a quantum network allows one to transfer a quantum state between two distant nodes.
• a superconducting flux qubit with a decay rate of yq ⁇ kHz is available using the existing technology [30-32]. This decay rate jq is much smaller than that of the optical cavity.
• the fidelity T to successfully transfer the quantum state is limited by the decay rate yq of the flux qubit, is about T ⁇ e ⁇ yq ' d , where td is the time to complete the maximal transfer. Therefore, a large K ex but a small y q is preferable for a high fidelity transfer.
• the symmetric linear combination of both optical modes is hardly excited while the anti symmetric one is only weakly excited.
• Fig. 4 there is illustrated the time state evolution of the photonic coupling.
• the photonic excitation decays 41 from the optical cavity A and is collected by the optical fiber and then is transferred to the flux qubit in the node B via the optical cavity B.
• the photon escaping from the optical cavity enters into the environment but not couples to the optical fiber, or is lost in transit through the fiber, and is not collected by node B.
• the fidelity of the transfer can be lower.
• the line 41 shows the population of the excited state ⁇ e) A in node A;
• the lines 43, 45 show the population of the excited state ⁇ e) B .
• Fig. 5 illustrates schematically one form of setup for the microwave-optical interface node 50 for the hybrid flux-qubit cavity opto- magneto-mechanical system.
• Light is injected 51 into a Fabry-Perot micro-cavity 52 that comprises a rigid curved input mirror 53 and a smaller back mirror (cavity length L) 54, where the back mirror sits on a substrate containing a superconducting flux qubit 56.
• the back mirror 54 mediates qubit-optical coupling via a bulk-acoustic -wave mechanical resonance in the hundreds of MHz regime.
• This mechanical mode where the thickness t( ⁇ B ⁇ ) of the back mirror oscillates, modulates the resonance frequency of the optical cavity and can be resonantly driven by a magnetic field using a surrounding magnetostrictive material 57 such as Terfenol-D.
• This form of magnetic coupling is considerably stronger than that achievable using a piezoelectric coupling.
• the quantum state of the superconducting flux qubit can then be made to interact with the optical field.
• This configuration is not restricted for operation at a particular optical wavelength and can be operated at the telecommunications wavelength of l,550nm.
• group 11- VI crystaline mirror materials such as magnesium selenide, simultaneously provide high mechanical quality and high optical reflectivity at this lower wavelength [33].
• the resulting interface node provides a design for an individual node based on a
• Fabry-Perot (FP) optical microcavity which is magnetically coupled to a nearby flux-qubit.
• the arrangement also provides a relatively strong magnetic coupling between the mechanics and flux qubit.
• the magneto-mechanical actuation can be achieved by using a collar of magneto- strictive material (e.g. Terfenol-D) 57, surrounding the moving mirror.
• magneto- strictive material e.g. Terfenol-D
• the collar exerts stress on the mirror, coupling to the BAW mode.
• Large effective magneto-mechanical coupling strength ⁇ ⁇ 1.2GHz can be provided.
• the transition frequency of a flux qubit is much higher than that of a mechanical resonator. This large frequency difference prevents the quantum information exchange between them.
• a coherent magnetic field . (t) is applied to strongly drive the flux qubit. As a result, the flux qubit oscillates at a Rabi frequency which matches the mechanical resonance frequency and this enhances their mutual coupling by several orders of magnitude [22].
• the available enhancement of the zero -point optomechanical coupling is limited by the usable photon number ⁇ 3 ⁇ 4
• inductive coupling can be used between the SQ and MR.
• inductive coupling between the SQ and MR is achieved by attaching a permanent magnet to the MR that is in close proximity to an electrical inductor that forms part of the electrical circuit with the SQ.
• the inductive coupling between the SQ and MR is achieved by using two inductors, one placed on the MR and the other forming part of the microwave circuit.
• configurations other than those specified above are used to achieve the inductive coupling between the SQ and MR.
• more than one permanent magnet is used to achieve the inductive coupling between the SQ and MR.
• more than two inductors are used to achieve the inductive coupling between the SQ and MR.
• the inductive coupling between the SQ and MR allows the state of the electrical circuit to modify the mechanical motion, which in turn modifies the optical field, thus enabling microwave -to-optical state transfer.
• optical coupling of distant superconducting circuits opens up a new paradigm which may allow for quantum repeaters, distributed quantum computation, quantum sensing and quantum networking over large spatial scales.
• the preferred embodiments provide for the facilitation of quantum repeaters making use of magneto-mechanical coupling between a flux qubit and micro-optical cavity.
• any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others.
• the term comprising, when used in the claims should not be interpreted as being limitative to the means or elements or steps listed thereafter.
• the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B.
• Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.
• exemplary is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment” is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.
• Coupled may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

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• 2015
  • 2015-02-25 WO PCT/AU2015/000107 patent/WO2015127498A1/en active Application Filing

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