Patent Description:
Superconducting qubits operate in the microwave regime of the electromagnetic spectrum. At microwave frequencies, microwave transmission lines (i.e., coaxial cable, striplines in printed circuit boards) are very lossy (~ <NUM> dB/foot attenuation). These losses prevent quantum information from being transported far. For example, the losses preclude quantum information from being transported outside of the dilution refrigerator environment using microwave transmission lines. Optical transduction converts a microwave photon to optical frequency (i.e., telecommunication range ~ <NUM>). In this regime of the electromagnetic spectrum, photons may propagate virtually lossless (~ <NUM> dB/km) through an optical fiber or free space. However, the materials and operation for qubits and optical transducers are often incompatible. <NPL>) discloses developing a packaging scheme that meets all of the requirements for operation of solid-state qubits in a cryogenic environment can be a formidable challenge. In this article, we discuss work being done in our group as well as in the broader community, focusing on the role of 3D integration and packaging in quantum processing with solid-state qubits. United States Patent Application Publication <CIT>, <NPL>) discloses a cryogenic electronic package includes a first superconducting multichip module ( SMCM ) , a superconducting interposer , a second SMCM and a superconducting semi conductor structure. The interposer is disposed over and coupled to the first SMCM , the second SMCM is disposed over and coupled to the interposer , and the superconducting semiconductor structure is disposed over and coupled to the second SMCM. The second SMCM and the superconduct ing semiconductor structure are electrically coupled to the first SMCM through the interposer. A method of fabricating a cryogenic electronic package is also provided.

Therefore, there is a need in the art to address the aforementioned problem.

Viewed from a first aspect, the present invention provides a system for optical transduction of quantum information, in accordance with independent claim <NUM>.

Viewed from a further aspect, the present invention provides a method for performing optical transduction of quantum information, in accordance with independent claim <NUM>. The dependent claims advantageous define embodiments of the invention.

The present invention will now be described, by way of example only, with reference to preferred embodiments, as illustrated in the following figures:.

<FIG> is a schematic illustration of a system <NUM> for optical transduction of quantum information according to an embodiment of the current invention. The system <NUM> includes a qubit chip <NUM> comprising a plurality of data qubits <NUM>, <NUM>, <NUM> configured to operate at microwave frequencies. The system <NUM> includes a transduction chip <NUM> spaced apart from the qubit chip <NUM>. The transduction chip <NUM> includes a microwave-to-optical frequency transducer (not shown in <FIG>; see <FIG>). The system <NUM> includes an interposer <NUM> coupled to the qubit chip <NUM> and the transduction chip <NUM>. The interposer <NUM> includes a dielectric material <NUM> comprising a plurality of superconducting microwave waveguides <NUM>, <NUM>, <NUM> formed therein. The plurality of superconducting microwave waveguides <NUM>, <NUM>, <NUM> is configured to transmit quantum information from the plurality of data qubits <NUM>, <NUM>, <NUM> to the microwave-to-optical frequency transducer on the transduction chip <NUM>. The microwave-to-optical frequency transducer is configured to transduce the quantum information from the microwave frequencies to optical frequencies. Although the embodiment of <FIG> shows an example having a particular number of data qubits, microwave-to-optical frequency transducers, and superconducting microwave waveguides, the embodiments of the invention are not limited to these particular numbers. Embodiments of the invention could include more or fewer data qubits, microwave-to-optical frequency transducers, and superconducting microwave waveguides.

According to an embodiment of the current invention, the microwave-to-optical frequency transducer is further configured to transduce quantum information from optical frequencies to microwave frequencies, and the plurality of superconducting microwave waveguides <NUM>, <NUM>, <NUM> is configured to transmit the quantum information from the microwave-to-optical frequency transducer on the transduction chip to the plurality of data qubits <NUM>, <NUM>, <NUM>.

As shown in <FIG>, the interposer <NUM> according to an embodiment of the invention includes a first surface <NUM> and a second surface <NUM> opposite the first surface <NUM>. The qubit chip <NUM> is coupled to the first surface <NUM> of the interposer <NUM>, and the transduction chip <NUM> is coupled to the second surface <NUM> of the interposer <NUM>.

According to an embodiment of the invention, the qubit chip is bonded to the interposer. In <FIG>, the qubit chip <NUM> is bonded to the interposer <NUM> using a plurality of solder bumps <NUM>, <NUM>, <NUM>. The solder bumps <NUM>, <NUM>, <NUM> may be directly coupled to the superconducting microwave waveguides <NUM>, <NUM>, <NUM>, and capacitively coupled to the data qubits <NUM>, <NUM>, <NUM>. The solder bumps may be formed from a superconducting material, although the embodiments of the invention are not limited to solder bumps formed from superconducting materials. One example material for the solder bumps is indium. Embodiments of the current invention are not limited to the number of solder bumps shown in the example illustrated in <FIG>.

According to an embodiment of the invention, the transduction chip is bonded to the interposer. In <FIG>, the transduction chip <NUM> is bonded to the interposer <NUM> using a plurality of solder bumps <NUM>, <NUM>, <NUM>. The solder bumps <NUM>, <NUM>, <NUM> couple the microwave-to-optical frequency transducer to the superconducting microwave waveguides <NUM>, <NUM>, <NUM>. The system <NUM> according to an embodiment of the present invention may include multiple qubit chips and transduction chips. The qubit chips and transduction chips may be bonded to a single interposer, or to multiple interposers.

The system according to an embodiment of the current invention enables the transfer of quantum information from a superconducting qubit chip through superconducting waveguides embedded in a dielectric interposer to a chip that performs optical transduction. The system separates stray light fields generated by microwave-to-optical transducers disposed on the transduction chip from the data qubits on the superconducting qubit chip through a packaging solution. Namely, data qubits may be formed on one chip, while a microwave-to-optical transducer may be formed on another chip. Thus, materials processing steps are separated between the qubit chip and the optical transduction chip. The data qubits on the qubit chip may be fabricated using materials and processes that optimize qubit coherence. Meanwhile, the transduction chip may be fabricated using materials and processes that facilitate microwave-to-optical transduction, without impacting the quality of the data qubits.

The system may also include qubits on the transduction chip. In this case, the qubit chip may possess qubits of high quality, while qubits on the transduction chip need only have lifetimes greater than transduction time, which ranges from <NUM> ns to <NUM>. Further, substrates such as electro-optic or piezoelectric materials that may be useful for forming a transduction chip are often not compatible with high qubit lifetimes. It is also difficult to fabricate long-lived qubits on silicon on insulator (SOI), which is often used as a transduction substrate. Qubits formed on SOI often have T1 and T2 times on the order of <NUM>. Processing techniques that are useful for forming microwave-to-optical transducers, such as multiple lithographic steps, may degrade qubit lifetime due to junction annealing and/or introduction of two-level systems (i.e., dielectric loss). By separating data qubits and microwave-to-optical transducers on different chips, optimal processing techniques can be used to form each chip and the structures included thereon.

According to an embodiment of the current invention, the microwave-to-optical frequency transducer comprises a microwave waveguide coupled to a device configured to operate in an optical frequency domain. <FIG> is a schematic illustration of a transduction chip <NUM>. The transduction chip <NUM> includes a microwave-to-optical frequency transducer <NUM> that includes a microwave waveguide <NUM> coupled to a device <NUM> configured to operate in an optical frequency domain. The device <NUM> may be, for example, an optical resonator in the shape of a ring, an oval, a race track, or a double figure <NUM>. The device <NUM> may be, for example, a bulk acoustic wave resonator, a mechanical coupler, or a membrane. The transduction chip <NUM> may also include an optical pump line <NUM> coupled to the device <NUM>. The optical pump line <NUM> is configured to transmit quantum information as an optical-frequency signal.

<FIG> is a schematic illustration of a qubit chip <NUM> according to an an aspect of the present disclosure, useful for understanding the claimed invention. The qubit chip <NUM> includes a data qubit <NUM> configured to operate at microwave frequencies.

<FIG> is a schematic illustration of an interposer <NUM> according to an an aspect of the present disclosure, useful for understanding the claimed invention. The interposer <NUM> includes a dielectric material <NUM> including a superconducting microwave waveguide <NUM> formed therein. According to an embodiment of the present invention, the dielectric material <NUM> includes one or more of a printed circuit board, an organic laminate, a silicon chip, a ceramic, a glass-reinforced epoxy laminate material such as FR-<NUM>, duroid, or polyether ether ketone (PEEK), for example. According to an embodiment of the present invention, the superconducting microwave waveguide <NUM> may be formed from one or more of niobium, aluminum, tin, electroplated rhenium, or indium, for example.

<FIG> is a schematic illustration of the interposer coupled to the transduction chip and the qubit chip according to an embodiment of the current invention. The superconducting microwave waveguide <NUM> is configured to transmit quantum information from the data qubit <NUM> to the microwave-to-optical frequency transducer <NUM> on the transduction chip. Although <FIG> and <FIG> show a qubit chip that has a single data qubit <NUM>, the qubit chip according to an embodiment of the present invention includes a plurality of data qubits. Although <FIG> and <FIG> show an interposer that has a single superconducting microwave waveguide <NUM>, the interposer according to an embodiment of the present invention may include a plurality of superconducting microwave waveguide.

According to an embodiment of the present invention, the transduction chip includes a plurality of transduction qubits. <FIG> is a schematic illustration of a transduction chip <NUM> that includes two transduction qubits <NUM>, <NUM>. Each of the transduction qubits <NUM>, <NUM> is coupled to a microwave-to-optical frequency transducer <NUM>, <NUM>. The microwave-to-optical frequency transducers <NUM>, <NUM> according to an embodiment of the invention each include a microwave waveguide <NUM>, <NUM> coupled to a resonator <NUM>, <NUM> configured to operate in an optical domain. The resonators <NUM>, <NUM> may have a variety of shapes, for example, a ring, a race track, or a figure <NUM>. The resonators <NUM>, <NUM> are each coupled to an optical pump line <NUM>, <NUM>.

<FIG> is a schematic illustration of an interposer <NUM> according to an embodiment of the current invention. The interposer <NUM> includes a dielectric material <NUM> comprising two superconducting microwave waveguides <NUM>, <NUM> formed therein.

<FIG> is a schematic illustration of the interposer <NUM> of <FIG> coupled to the transduction chip <NUM> of <FIG> and to a qubit chip, such as the qubit chip <NUM> shown in <FIG>. The superconducting microwave waveguides <NUM>, <NUM> are configured to transmit quantum information from the data qubit <NUM> to the microwave-to-optical frequency transducers <NUM>, <NUM> via the transduction qubits <NUM>, <NUM>. The microwave waveguides <NUM>, <NUM> transmit quantum information from the data qubit <NUM> to the transduction qubits <NUM>, <NUM> via microwave photons. The embodiments of the invention are not limited to the particular number of data qubits, superconducting microwave waveguides, and transduction qubits shown in the example illustrated in <FIG>.

According to an embodiment of the current invention, each of the plurality of data qubits has a relaxation time (T1) and a coherence time (T2) sufficient for performing quantum computation. The data qubits according to an embodiment of the current invention may have T1 and T2 times that are greater than <NUM>. The data qubits according to an embodiment of the current invention may have T1 and T2 times on the order of <NUM> or greater.

According to an embodiment of the current invention, each of the plurality of transduction qubits has a relaxation time and a coherence time that exceeds a transduction time of the microwave-to-optical frequency transducer. For example, if the time required for microwave-to-optical frequency transduction is about <NUM> ns - <NUM>, then the transduction qubit may have T1 and T2 times on the order of about <NUM> or more. According to an embodiment of the current invention, the transduction time of the microwave-to-optical frequency transducer is less than <NUM>. According to an embodiment of the invention, the transduction qubits have T1 and T2 times that are less that the T1 and T2 times of the data qubits.

According to an embodiment of the current invention, the transduction chip includes a substrate that includes one or more of an electro-optic material, a piezoelectric material, or a silicon-on-insulator substrate. According to an embodiment of the invention, the microwave-to-optical frequency transducer comprises an optomechanical system such as, for example, a membrane.

As an alternative to the configuration shown in <FIG>, the qubit chip and the transduction chip may be coupled to the same surface of the interposer. <FIG> is a schematic illustration of a qubit chip <NUM> and a transduction chip <NUM> coupled to the same surface <NUM> of an interposer <NUM>.

<FIG> is a flowchart that illustrates a method <NUM> for performing optical transduction of quantum information. The method <NUM> includes providing a qubit chip including a plurality of data qubits configured to operate at microwave frequencies <NUM>. The method <NUM> includes transferring quantum information from the plurality of data qubits to a transduction chip spaced apart from the qubit chip, the transduction chip including a microwave-to-optical frequency transducer <NUM>. The method <NUM> includes performing microwave-to-optical frequency transduction of the quantum information while shielding the plurality of data qubits from stray light fields using a dielectric interposer disposed between the qubit chip and the transduction chip <NUM>, and outputting the quantum information as an optical-frequency signal <NUM>.

<FIG> is a schematic illustration of a quantum computer <NUM> according to an embodiment of the present invention. The quantum computer <NUM> includes a refrigeration system under vacuum comprising a containment vessel <NUM>. The quantum computer <NUM> includes a qubit chip <NUM> contained within a refrigerated vacuum environment defined by the containment vessel <NUM>. The qubit chip <NUM> includes a plurality of data qubits <NUM>, <NUM>, <NUM> configured to operate at microwave frequencies. The quantum computer <NUM> includes a transduction chip <NUM> contained within the refrigerated vacuum environment defined by the containment vessel <NUM>. The transduction chip <NUM> is spaced apart from the qubit chip <NUM> and includes a microwave-to-optical frequency transducer. The quantum computer <NUM> includes an interposer <NUM> contained within the refrigerated vacuum environment defined by the containment vessel <NUM>. The interposer <NUM> is coupled to the qubit chip <NUM> and the transduction chip <NUM>. The interposer <NUM> includes a dielectric material <NUM> including a plurality of superconducting microwave waveguides <NUM>, <NUM>, <NUM> formed therein. The plurality of superconducting microwave waveguides <NUM>, <NUM>, <NUM> is configured to transmit quantum information from the plurality of data qubits <NUM>, <NUM>, <NUM> to the microwave-to-optical frequency transducer on the transduction chip <NUM>, and the microwave-to-optical frequency transducer is configured to transduce the quantum information from the microwave frequencies to optical frequencies.

According to an embodiment of the present invention, the dielectric material <NUM> includes one or more of a printed circuit board, an organic laminate, a silicon chip, a ceramic, a glass-reinforced epoxy laminate material such as FR-<NUM>, duroid, or polyether ether ketone (PEEK). According to an embodiment of the present invention, the microwave-to-optical frequency transducer includes a microwave waveguide coupled to a device configured to operate in an optical frequency domain. The transduction chip <NUM> further includes an optical pump line coupled to the device configured to operate in an optical frequency domain, such as the optical pump line <NUM> in <FIG>. The optical pump line may be configured to transmit the quantum information as an optical-frequency signal from the refrigerated vacuum environment defined by the containment vessel <NUM> to an exterior of the containment vessel <NUM>. Alternatively or additionally, the optical pump line may be configured to transmit the quantum information as an optical-frequency signal from the transduction chip <NUM> to a second transduction chip coupled to a second qubit chip.

The quantum computer according to an embodiment of the current invention may include a plurality of data qubit chips, transduction chips, and interposers. Further, the embodiments of the invention are not limited to the particular number of data qubits, microwave-to-optical frequency transducers, and superconducting microwave waveguides shown in <FIG>.

Claim 1:
A system (<NUM>) for optical transduction of quantum information, comprising:
a qubit chip (<NUM>) comprising a plurality of data qubits (<NUM>) configured to operate at microwave frequencies;
a transduction chip (<NUM>, <NUM>) spaced apart from said qubit chip, said transduction chip comprising a microwave-to-optical frequency transducer (<NUM>, <NUM>, <NUM>), wherein said microwave-to-optical frequency transducer comprises a microwave waveguide (<NUM>, <NUM>, <NUM>) coupled to a device (<NUM>, <NUM>, <NUM>) configured to operate in an optical frequency domain, wherein said device comprises an optical resonator (<NUM>), where said transduction chip further comprises an optical pump line (<NUM>, <NUM>, <NUM>) coupled to said optical resonator, wherein said optical pump line is configured to transmit said quantum information as an optical-frequency signal; and
an interposer (<NUM>, <NUM>) coupled to said qubit chip and said transduction chip, said interposer comprising a dielectric material (<NUM>, <NUM>) comprising a plurality of superconducting microwave waveguides (<NUM>, <NUM>, <NUM>) formed therein, wherein said plurality of superconducting microwave waveguides is configured to transmit quantum information from said plurality of data qubits to said microwave-to-optical frequency transducer, and wherein said microwave-to-optical frequency transducer is configured to transduce said quantum information from said microwave frequencies to optical frequencies,
wherein said transduction chip (<NUM>, <NUM>) comprises a plurality of transduction qubits (<NUM>, <NUM>), and
wherein said transduction chip (<NUM>, <NUM>) further comprises a plurality of microwave-to-optical frequency transducers (<NUM>, <NUM>, <NUM>), and wherein each of said plurality of transduction qubits (<NUM>, <NUM>), is coupled to one of said plurality of microwave-to-optical frequency transducers (<NUM>, <NUM>, <NUM>),
in a one-to-one coupling between said plurality of transduction qubits (<NUM>, <NUM>) and said plurality of microwave-to-optical frequency transducers (<NUM>, <NUM>, <NUM>),
wherein said superconducting plurality of microwave waveguides (<NUM>, <NUM>, <NUM>) is configured to transmit quantum information from said plurality of data qubits (<NUM>) to said plurality of transduction qubits via microwave photons.