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Glass-based quantum photonic packaging

By Wojciech Lewoczko-Adamczyk, Henning Schröder [Fraunhofer IZM]
T he ongoing second quantum

revolution is powered by
such quantum-mechanical
phenomena as superposition, quantum
ent a nglement, a nd i nter ference.
Superposition suggests that a quantum
particle, isolated from its environment,
can exist at the same time in any
combination of quantum states: different
energy levels, spin, polarization, or
even positions in space. Compared to
the conventional bit, the basic building
block of our digital world, which only Figure 1: Building blocks of hybrid integrated quantum systems.
has two discrete states – 0 or 1 – the and “classical” integrated photonics reasons, hybrid platforms combining
quantum bit, or qubit, has an infinite may provide guidelines and solutions different photonic and electronic
number of possible identities. This here. The most advanced in this matter integration technologies will dominate
range of possible states for every are quant um photonic integrated over monolithic integration of quantum
qubit was recognized as the potential circuits (QPICs), the manufacturing devices over the next few years [3].
basis for quantum computing and and packaging of which is based on
quantum simulation. The entanglement modern nanofabrication approaches Glass-based photonic packaging
phenomenon – the ability to remotely [2] developed for data communication. We have added our own piece to the
detect the state of one particle by However, monolithic photonic platforms hybrid quantum puzzle by providing
measuring the state of its twin – forms can hardly meet the stringent demands integration technologies and packaging
the basis for secure, bug-proof quantum of most quantum applications. First of solutions for quantum systems built on
communication and quantum-based all, the optical wavelengths of interest years of experience with glass-based
noninvasive imaging technologies for quantum technologies lie at visible electro-optic circuit boards (EOCBs)
(ghost imaging). Finally, the outcome to the near-infrared (NIR) range, well developed for data communication
of interferometric measurements reacts below the transparency window of [4, 5], a nd w it h st r uc t u r i ng a nd
to even the tiniest outside forces, such silicon photonics. Therefore, several stacking of thin glasses for micro-
as electrical or magnetic fields, Earth’s different materials (silicon nitride, photonic assembling [6]. In this section
acceleration at the specific time and lithium niobate, aluminum nitride, we present advantages of glass as a
place, or simply the passing of time. diamond, silica, glass, to name a few) board-level packaging platform and
Quantum sensors can use this sensitivity are currently being investigated for their point out some challenges that remain
to outperform conventional sensors, ability to be suitable carriers for optical to be overcome.
as they do not have to be calibrated. quantum information. Because single Glass as a substrate material for
Rather, the measured data are strictly photons in quantum communication electro-optical applications has many
related to several well-known and protocols are not amplified (or cloned), benefits compared to conventional
absolute constants of nature. low optical loss is a major criterion packaging materials like silicon,
of choice for the waveguide material. ceramic or organic laminates, because
Hybrid integration approach Second, future quantum devices must of its excellent dielectric properties and
T he potential of new quant u m involve coupling of photons to quantum optical transparency in a wide spectral
technologies is enormous as recognized memories realized by atomic (or solid- range. Furthermore, the integration
by several market studies [1]. However, state, atom-like) or molecular qubits potential of glass is superior because
the forthcoming challenge is to make hosted by other classes of materials of its dimensional stability under
the leap from highly complicated in or hot vapors for which hermetic thermal load (compared to polymers or
handling, bulky, and power-hungry packaging approaches are necessary. metals) and its coefficient of thermal
custom laboratory systems, to devices Lastly, integration of active opto- expansion (CTE) matches sufficiently
that can be scalable and cost-effectively electronic components, such as light to that of silicon integrated circuits
produced and are reliable for use in the sources, photodiodes and modulators, (ICs) or other optical components and
real world. Experience from chip-level completes the spectrum of required optics holders made of glass. In terms
integration known from electronics building blocks (Figure 1). For these of cost efficiency and methods to

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