draft-kaws-qirg-advent-00.xml

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<front>
  <title abbrev='Advertising EntCap'>
    Advertising Entanglement Capabilities in Quantum Networks
  </title>

  <author initials="K." surname="Kompella" fullname="Kireeti Kompella">
    <organization>Juniper Networks, Inc.</organization>
    <address>
      <postal>
	<street>1133 Innovation Way</street>
	<city>Sunnyvale</city>
	<region>CA</region>
	<code>94089</code>
	<country>USA</country>
      </postal>
      <email>kireeti.kompella@gmail.com</email>
    </address>
  </author>

  <author initials="M." surname="Aelmans" fullname="Melchior Aelmans">
    <organization>Juniper Networks, Inc.</organization>
    <address>
      <postal>
	<street>Boeing Avenue 240</street>
	<city>Schipol-Rijk</city>
	<region>PZ</region>
	<code>1119</code>
	<country>The Netherlands</country>
      </postal>
      <email>melchior@aelmans.eu</email>
    </address>
  </author>

  <author initials="S." surname="Wehner" fullname="Stephanie Wehner">
    <organization>QuTech</organization>
    <address>
      <postal>
	<street>Van der Waalsweg 122</street>
	<city>Delft</city>
	<region>LC</region>
	<code>2611</code>
	<country>The Netherlands</country>
      </postal>
      <email>s.d.c.wehner@tudelft.nl</email>
    </address>
  </author>

  <author initials="C." surname="Sirbu" fullname="Cristian Sirbu">
    <organization>Redbit Networks</organization>
    <address>
      <postal>
	<street></street>
	<city>Dublin</city>
	<region></region>
	<code></code>
	<country>Republic of Ireland</country>
      </postal>
      <email>cristian@redbit.network</email>
    </address>
  </author>
  <date/>

  <area>Routing</area>
  <workgroup>QIRG</workgroup>

  <keyword>Quantum Internet</keyword>
  <keyword>EPR pair</keyword>
  <keyword>entanglement</keyword>
  <keyword>fidelity</keyword>
  <keyword>multi-hop entangled pair</keyword>

  <abstract>
    <t>
      This document describes the use of link-state routing protocols
      on classical links in Quantum Networks. It contains proposals
      for additions to the IS-IS and OSPF protocols in order for them
      to transport relevant information for a Quantum Network,
      specifically, for the creation and manipulation of entangled
      pairs. The document will describe some of the necessary
      attributes and some suggestions of how this information may be
      used.
    </t>
    <t>
      No Schrodinger’s cats were harmed in the creation of this document.
    </t>
  </abstract>

  <note title="Requirements Language">
    <t>
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
      "OPTIONAL" in this document are to be interpreted as described
      in <xref target="RFC2119"/>.
    </t>
  </note>
</front>

<middle>
  <section title="Introduction" anchor='intro'>
    <t>
      Quantum networking is an emerging field using the strange (even
      counterintuitive) properties of quantum mechanics to bring new,
      useful capabilities to networking.  One of these is
      “entanglement” <xref target='QEnt'/>, where the state of a group
      of particles must be described as a unit -- it cannot be
      decomposed to the state of each particle independently.
      Entangled pairs (often called EPR pairs, abbreviated here as EP)
      of particles can be used for quantum teleportation <xref
      target="QTel"/> and for quantum key distribution (QKD) <xref
      target='QKD'/>.
    </t>
    <t>
      A Quantum Network consists of quantum nodes and links. Here, we
      will be concerned with controllable quantum nodes (CQN) that
      allow control decisions. We posit a classical network parallel
      to the quantum network, with classical nodes (CN) and links.  A
      classical node is colocated with a quantum node; a classical
      link may be a fiber or wavelength parallel to the corresponding
      quantum link.  Such a classical link is required by most quantum
      methods to create EPs deterministically or in a heralded
      fashion, where the creation of EPs is deterministic conditioned
      on a specific signal.  To make useful decisions, it is desirable
      to augment this data to describe the capabilities and states of
      quantum nodes and links.
    </t>
    <t>
      This document proposes to carry entanglement capability data as
      Type Length Values (TLVs) over IS-IS or OSPF link-state
      advertisements over the corresponding classical network.  A
      subset of the CQNs may run quantum applications such as QKD;
      these nodes may want to initiate multihop EPs.
    </t>
    <t>
      Once an EP is created, the state of one particle (“quantum bit”
      or qubit) of an EP can be transferred to another qubit within
      the same QN by a process known as swapping or a SWAP gate (<xref
      target='QInt'/>).  Also, several pairs of imperfectly entangled
      qubits can be “distilled” (<xref target='QDist'/>) to fewer but
      “better entangled” qubits.
    </t>
    <t>
      Long distance entanglement can be produced from piecewise short
      distance entanglement: Given an EP between CQN A and CQN B, and
      another EP between CQN B and CQN C, one can create an EP between
      CQN A and CQN C by a process known as an “entanglement swap”.
      These operations can be used to manipulate EPs to improve their
      lifetimes or their quality, or to create multihop EPs.
      Physically, qubits can be realized in many ways.  For example,
      they can be represented by the energy levels of Nitrogen Vacancy
      (NV) Centers in diamond (<xref target='NVD'/>, <xref
      target='NVDD'/>).  Logically, a qubit can be classified as a
      “communication qubit”, a “traveling qubit” or a “storage qubit”.
    </t>
    <t>
      This document primarily discusses the exchange of quantum
      capabilities over a classical network.  Some illustrative
      examples of how these capabilities can be used in a quantum
      network may be given, but this document should not be considered
      authoritative on these procedures.
    </t>

    <section title='Definitions and Notation'>
      <t>
	The following terms are used in this document:
	<list style="hanging">
	  <t hangText='Quantum link:'>
	    A quantum link is a connection transporting traveling
	    qubits, typically photons.  This could be a physical link.
	    This document does not describe the usage of this link.
	  </t>
	  <t hangText='Classical link:'>
	    A classical link is a connection transporting packets.
	    This could be a physical link.  The proposed extensions in
	    this document use these links to exchange capabilities.
	  </t>
	  <t hangText="Controllable Quantum Node (CQN):">
	    A controllable quantum node is a quantum device consisting
	    of at least one qubit, capable of performing (a subset of)
	    the following operations described in detail below:
	    storing qubits for some amount of time, performing quantum
	    operations such as entanglement distillation and
	    entanglement swapping, and producing entanglement between
	    the nodes and traveling qubits. The latter are generally
	    realized using photons over fibers or through free space.
	  </t>
	  <t>
	    The term controllable refers to the fact that external
	    control in software is capable of selecting the desired
	    operations and qubits to use. Such nodes can be quantum
	    repeaters that allow choices of operations to be made, as
	    well as quantum end nodes capable of executing complex
	    application protocols <xref target='QKD'/>.  Quantum
	    repeaters that merely allow timing control, such as
	    automatic entanglement swapping whenever qubits arrive in
	    a specific timing interval, will not be referred to as
	    CQN.  Such automated repeaters can be seen as lying at the
	    quantum physical layer and do not enter routing or other
	    decision making, apart from being switched on or off, and
	    hence are not relevant to advertisement protocols like the
	    ones considered here.
	  </t>
	  <t hangText="Quantum end node (QEN):">
	    In this document, a quantum end node <xref target='QKD'/>
	    is one of a pair of quantum nodes forming a entanglement
	    via a sequence of zero or more CQNs.  Quantum end nodes
	    typically run a higher-layer quantum application such as
	    QKD.
	  </t>
	  <t hangText="Communication qubit:">
	    A qubit is called a communication qubit if it is possible
	    to produce entanglement between this qubit and a traveling
	    photon. This can be done by emission from the quantum
	    node, that is, entanglement is produced between the qubit
	    and the photon which is emitted from the quantum
	    node. This process has been demonstrated in a number of
	    physical systems that can be used as quantum nodes such as
	    NV in diamond (<xref target='NVD'/>, <xref
	    target='NVDD'/>), Ion Traps (<xref target='IonTrap'/>) and
	    Neutral Atoms (<xref target='NAtom'/>).  An example of a
	    communication qubit is the electron spin of the NV in
	    diamond system (<xref target='NVC'/>).  Entanglement
	    between a communication qubit and traveling photons can
	    also be produced by absorption.  Examples include atomic
	    ensemble memories (<xref target='QAEM'/>).
	  </t>
	  <t>
	    A communication qubit c at CQN A is denoted by c@A, or
	    simply c (if the node A is understood).
	  </t>
	  <t hangText='Storage qubit:'>
	    A qubit is called a storage qubit if the node has the
	    capability to use this qubit as a (temporary) quantum
	    memory, but the qubit cannot serve as a communication
	    qubit. To make storage qubits useful a node is required to
	    possess the ability to transfer the state of a
	    communication qubit to a storage qubit. An example of a
	    storage qubit is the nuclear spin in the NV in diamond
	    system <xref target='NVD'/>.
	  </t>
	  <t>
	    A storage qubit s at node B is denoted s@B.
	  </t>
	  <t hangText="Entangled Pair (EP):">
	    An entangled pair is a special state of two qubits, known
	    as an EPR pair <xref target='QEnt'/>.  An entangled pair
	    of qubits c@A and c@B is denoted [[c@A, c@B]].
	  </t>
	  <t>
	    The process of entangling two particles c@A and c@B is
	    denoted as follows:
	    <figure>
	      <artwork align='left'>
ent(c@A, c@B) -&gt; [[c@A, c@B]]
	      </artwork>
	    </figure>
	    ent(c@A, c@B) may take time T and succeed with probability
	    P, and yield an entangled pair [[c@A, c@B]] of fidelity F.
	  </t>
	  <t hangText='Fidelity:'>
	    A measure of the quality of the entanglement of an EP
	    (xref target='QFid'/>).  Fidelity lies in the interval [0,
	    1] where a higher value indicates better quality; usable
	    fidelity values lie in the half-open interval (0.5, 1].
	  </t>
	  <t hangText='Swap:'>
	    Two qubits located in the same CQN can interchange states
	    (<xref target='QDist'/>).  For example, the states of a
	    communication qubit and a storage qubit at A can be
	    swapped as follows:
	    <figure>
	      <artwork align='left'>
swap(c@A, s@A)
	      </artwork>
	    </figure>
	    If c@A was entangled with c@B, the result is that s@A is
	    now entangled with c@B.
	  </t>
	  <t hangText='Distillation:'>
	    Distillation is the process of turning a large number of
	    weakly entangled states into a smaller number of highly
	    entangled states (<xref target='QDist'/>).
	  </t>
	  <t>
	    For example, EPs [[c1@A, c1@B]] and [[c2@A, c2@B]] of
	    fidelities F1 and F2 respectively may be distilled as
	    follows:
	    <figure>
	      <artwork align='left'>
dist([[c1@A, c1@B]], [[c2@A, c2@B]]) -&gt; [[c3@A, c3@B]]
	      </artwork>
	    </figure>
	  </t>
	  <t>
	    If distillation is successful, the fidelity F3 of [[c3@A,
	    c3@B]] will be higher than F1 and F2.
	  </t>
	  <t hangText='Entanglement Swap:'>
	    Given two EPs [[c@A, c1@B]] and [[c2@B, c@C]], one can perform
	    an entanglement swap:
	    <figure>
	      <artwork align='left'>
entSwap([[c@A, c1@B]], [[c2@B, c@C]]) -&gt; [[c@A, c@C]]
	      </artwork>
	    </figure>
	    to create a new EP between q@A and q@C.  This is how
	    "multihop" EPs are created from a sequence of "single-hop" EPs.
	  </t>
	  <t>
	    The swap operation can also be used within a CQN.  A
	    possible use case is when there aren't enough
	    communication qubits to create the needed EPs.  If, in the
	    above example, B doesn't have two communication qubits c1
	    and c2, the following can be done:
	    <figure>
	      <artwork align='left'>
ent(c@A, c@B)  -&gt; [[c@A, c@B]]	# entangle
swap(c@B, s@B) -&gt; [[c@A, s@B]]	# swap EP to storage qubit
ent(c@B, c@C)  -&gt; [[c@B, c@C]]	# use freed up qubit c@B
swap(s@B, c@B) -&gt; [[c@A, c@C]]	# create multihop EP
	      </artwork>
	    </figure>
	  </t>
	</list>
      </t>
    </section>
  </section>

  <section title="Motivation">
    <t>
      Consider the following (very simple) quantum network consisting
      of QENs A and B, and CQNs X, Y, Z, U, V.  The goal is to create
      an EP between qubits at A and at B, perhaps for the high-level
      task of QKD between A and B.
      <figure>
	<artwork align='center'>
      X - Y - Z 
    .           .         
 A                 B                A, B: QEN
    .           .       
       U --- V             X, Y, Z, U, V: CQNs
	</artwork>
      </figure>
    </t>
    <t>
      From A's point of view, here are a number of questions:
      <list style='numbers'>
	<t>
	  Is B reachable from A via quantum links that allow EP creation?
	</t>
	<t>
	  If so, along what sequence(s) of quantum nodes?
	</t>
	<t>
	  Can each pair of adjacent CQNs in this sequence form EPs?  If
	  so, how long will it take, and what fidelity can be
	  expected?
	</t>
	<t>
	  If each pair of adjacent CQNs successfully forms EPs of
	  sufficient fidelity, can these be swapped to form a multihop
	  EP between A and B?
	</t>
	<t>
	  If a multihop EP between A and B were to be formed, would it
	  be of good enough fidelity, or should a second multihop EP
	  be formed and the two EPs distilled into one high fidelity
	  EP?  How many times should this process be repeated?
	</t>
	<t>
	  If the overall answer is Yes, should A proceed via sequence
	  A, X, Y, Z, B, or sequence A, U, V, B?
	</t>
      </list>
    </t>
    <t>
      This document aims to provide all CQNs in a quantum network with
      the information they need to answer such questions, and to create
      EPs at their desired fidelity and speed.
    </t>
  </section>

  <section title="Theory of Operation">
    <t>
      A CQN contains one or more communication qubits and one or more
      storage qubits. Many proposals exist for producing EPs between
      remote quantum nodes (see for example <xref target='NVD'/>,
      <xref target='NVDD'/>, <xref target='IonTrap'/>, <xref
      target='QAEM'/>).  Abstractly, these result in the generation of
      EPs with fidelity F after an expected time t. To give an
      example, we describe the generation of EPs that has been
      implemented in NV in diamond (<xref target='NVD'/>), and Ion
      Traps (<xref target='IonTrap'/>). The largest distance for
      producing long-lived entanglement is presently 1.3kms (<xref
      target='NVDD'/>).  To entangle a pair of communication qubits,
      the QNs send carefully timed photons towards the HS.  If the
      process is successful, HS sends an OK message to both QNs.
    </t>
    <t>
      <figure>
	<artwork align='center'>
+----------+                                      +----------+
|          |  c-chan    +------------+    c-chan  |          |
| Control- | &lt;-------&gt;  | Heralding  |  &lt;-------&gt; |  Control-|
| lable    |            |  Station   |            |    lable |
| Quantum  | *~~~~~~~&gt;  |            |  &lt;~~~~~~~* |  Quantum |
| Node     |  q-chan    +------------+    q-chan  |     Node |
| A        |                                      |        B |
|          | &lt;----------------------------------&gt; |          |
+----------+    classical network control plane   +----------+
	</artwork>
      </figure>
    </t>
    <t>
      The classical network control plane is of particular interest
      here as it would be used by the proposed protocol to advertise
      and exchange information about the capabilities of the CQNs to
      generate entanglement. This classical channel exists between all
      CQNs and is shared with other application specific control and
      data plane traffic.
    </t>
    <section title="Multihop Entanglement">
      <t>
	<figure>
	  <artwork>
	         resulting entanglement
     *~~~~~~~~~~~~~~~~~~~~~~~~~~~~*
   +-+                            +-+                            +-+
   |A+----------------------------+B+----------------------------+C|
   +-+   A-B Link properties      +-+                            +-+
             [(F1,t1), (F2,t2)]    Node B properties:
                                   - Number of Communication Qubits
                                   - Number of Storage Qubits
                                   Node capabilities (operations):
                                   - Swap comm &lt;-&gt; storage
                                   - Entanglement swap
                                   - [(Distillation scheme, time)...]
	  </artwork>
	</figure>
      </t>
      <t>
	In the figure above, an example request for an entangled pair
	between nodes A and B will be affected by the following
	properties:
	<list style='symbols'>
	  <t>
	    A chosen combination of F(idelity) and t(ime) duration to
	    produce an entanglement at the respective Fidelity. These
	    parameters roughly equate to the quality of the link, the
	    accuracy with which the nodes can use the link, and the
	    delay in classical networking.
	  </t>
	  <t>
	    The actual capability of nodes A and B to make use of the
	    communication qubits.
	  </t>
	</list>
      </t>
      <t>
	A new EP creation between CQNs B and C will similarly be
	affected by the same parameters as above.
	<figure>
	  <artwork>
                                        resulting entanglement
     *~~~~~~~~~~~~~~~~~~~~~~~~~~~~* *~~~~~~~~~~~~~~~~~~~~~~~~~~~~*
   +-+                            +-+                            +-+
   |A+----------------------------+B+----------------------------+C|
   +-+                            +-+   B-C Link properties      +-+
                                            [(F1,t1), (F2,t2)]
	  </artwork>
	</figure>
      </t>
      <t>
	And finally, with an entanglement swap operation at node B
	(which is a node specific capability and has a specific
	duration) we end up with an A-C EP:
	<figure>
	  <artwork>
     *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*
   +-+                            +-+                            +-+
   |A+----------------------------+B+----------------------------+C|
   +-+                            +-+                            +-+
                    Node B entanglement swap operation
	  </artwork>
	</figure>
      </t>
    </section>
    <section title='Distillation'>
      <t>
	If a pair of CQNs A and B share a number of EPs of
	insufficient quality, they may be combined into a single EP of
	higher quality by distillation. To do so, these CQNs need to
	agree on which distillation scheme to use before distillation
	can proceed.  This does not necessarily need to be via
	communication between A and B, if one agrees upon a
	deterministic procedure of selecting one. This document
	suggests the following procedure:
	<list style='numbers'>
	  <t>
	    A and B look at the distillation schemes that both
	    advertise in common.
	  </t>
	  <t>
	    If there is none in common, stop.  Distillation is not
	    possible.
	  </t>
	  <t>
	    If there is a non-trivial subset in common, the first
	    scheme in the node with the lower router ID is to be used
	    by A and B.
	  </t>
	</list>
      </t>
      <t>
	Given a chosen distillation scheme (S,t,p), an additional time
	delay will be added for the actual operation: For a 2:1
	distillation scheme between nodes A and B, 2 EPs need to be
	produced followed by an operation on A and B that produces 1
	EP. This operation will take time some expected time t, and
	succeed with probability p.
	<figure>
	  <artwork>
     2:1 distillation (S,t,p)
  *~~~~~~~~~~~~~~~~~~~~~~~~~~~~*
  *~~~~~~~~~~~~~~~~~~~~~~~~~~~~*
+-+                            +-+                            +-+
|A+----------------------------+B+----------------------------+C|
+-+   A-B Link properties      +-+                            +-+
          [(F1,t1), (F2,t2)]
	  </artwork>
	</figure>
      </t>
    </section>
    <section title='Node Properties'>
      <t>
	We are interested in exposing the properties of CQNs (including
	QENs) to allow sophisticated decision making, for example in the
	creation of entanglement.  These properties include:
	<list style='numbers'>
	  <t>
	    Number of communication qubits.  The number of
	    communication qubits determines the number of entangled
	    pairs that the node can produce simultaneously.
	  </t>
	  <t>
	    Number of storage qubits
	  </t>
	  <t>
	    Possible operations, along with their execution time and
	    probability of success:
	    <list style='numbers'>
	      <t>
		Swap between communication and storage qubits
	      </t>
	      <t>
		Entanglement swap
	      </t>
	      <t>
		List of supported distillation schemes (in order of
		preference).
	      </t>
	    </list>
	  </t>
	</list>
      </t>
      <t>
	Note that several other parameters can be advertised, such as
	the T1 and T2 times for a qubit’s decoherence.  These are
	omitted for now, instead just giving the decay of the fidelity
	of an EP.  If deemed useful, T1 and T2 times can additionally
	be advertised.
      </t>
    </section>
    <section title='Link Properties'>
      <t>
	A list of (Fn,tn) pairs describing the tradeoffs of a possible
	entanglement produced by two nodes (the ends of said link): tn
	is the time to produce an entangled pair with fidelity Fn.
      </t>
    </section>
  </section>

  <section title='The (Ab)use of Protocols'>
    <t>
      The routing protocols IS-IS and/or OSPF could be used in order
      to advertise entanglement capabilities.  This section describes
      the additional data fields needed in order to facilitate the
      objective.
    </t>
    <section title='A Brief Primer on Link-state Protocols'>
      <t>
	This document suggests the use of a link-state protocol to
	distribute the capabilities of CQNs to create entanglement.
	This section offers a short introduction to link-state
	protocols for those not familiar with them.
      </t>
      <t>
	Consider a directed graph G=(V, E) with vertices (nodes) V and
	edges (links) E.  Consider also G'=(V', E'); there is a 1-1
	mapping from V' to V and from E' to E such that e1' =
	(v1', v2') is in E' iff e1 = (v1, v2) is in E and v1' maps
	to v1 and v2' maps to v2.  G' represents the quantum
	network; V' represents the set of CQNs, and E' the set of
	quantum links between pairs of CQNs; G represents a classical
	network parallel to G'; that is, each CQN v' has a
	corresponding classical node v.  v plays a dual role: it is the
	control node for v', and proxies on behalf of v' in the
	link-state protocol.
      </t>
      <t>
	The basic objective of a link-state protocol is to "flood"
	properties of nodes and (directed) links to all nodes in the
	network.  This is accomplished by means of "link-state
	advertisements" (LSAs) that each node originates and sends to
	its immediate neighbors.  The neighbors in turn send received
	LSAs to their own neighbors; this process repeats until every
	node receives every LSA (hence the term "flooding").  The
	focus of LSAs is the link properties (hence _link-state_
	advertisements), although node properties are also advertised.
	There are mechanisms to prevent looping of LSAs, and for
	reliable flooding.  There is also a sequence number by which a
	more recent update of an LSA can be identified as such, and a
	mechanism for "aging out" LSAs belonging to nodes no longer in
	the network.  In what follows, quantum node and link
	properties are added to the link-state advertisements of the
	corresponding classical node.  Note that link properties need
	not be symmetric; that is, the link properties of (v, w) need
	not be the same as those of (w, v).
      </t>
      <t>
	The net result of flooding is that every node has the same
	picture of the network (modulo LSAs in flight); in particular,
	each node knows the overall topology and connectivity of the
	network, and can use this information to make decisions.  In a
	classical network, such a decision could be to compute a
	shortest path; for the quantum network, it could be choosing a
	feasible path (i.e., sequence of CQNs) for a multihop
	entanglement.  Note that a node doesn't really know when it
	has complete and up-to-date information about the network; LSA
	updates may be originated at any time.  Usually, this is okay:
	for example, if a node v learns enough of the network to have
	a path to another node w, it can compute a multihop
	entanglement to w.  Subsequent updates may provide a more
	optimal (or higher probability) entanglement path.  There are
	heuristics one can apply to guess that the link-state database
	(LSDB) (i.e., the union of all LSAs) is complete-ish; however,
	as nodes (and links) can fail or disconnect, there really is
	no such thing as "the full LSDB".
      </t>
      <t>
	Each node v is identified by a "router ID" (an IP address
	uniquely allocated to v), denoted by rid(v).  A link L = (v,
	w) is identified by (rid(v), i) where i is an index allocated
	by v for L unique for each link emanating from v.  (L may also
	be identified by IP addresses, but we'll ignore that for now.)
	It is generally expected that a directed link (v, w) is
	matched by a link (w, v); if not, (v, w) is ignored from
	subsequent consideration; in particular, no link properties
	are advertised for this link by v.  Note that a pair of nodes
	may have multiple links between them; for simplicity, the
	notation will not be extended to indicate this.  We'll assume
	rid(v') = rid(v) and the index allocated to a quantum link
	e' is the same as that of the corresponding classical link e.
      </t>
      <t>
	Let v, w be a pair of neighboring nodes, and let L1 = (v, w)
	and L2 = (w, v) in E be directed links in opposite directions
	between v and w with identifiers (rid(v), i1) and (rid(w), i2)
	respectively (where i1 is the index allocated for L1 by v, and
	similarly for i2)).  As a first step in running a link-state
	protocol, v runs a "hello protocol" all its links; in
	particular, over L1.  Similarly, w will run the hello protocol
	over L2.  The hello protocol serves to exchange the indices i1
	and i2, and thus identify (rid(v), i1) as the reverse link of
	(rid(w), i2).  This allows both v and w to correlate the link
	properties of L1 and L2.  If the hello protocol fails between
	v and w, neither node includes link properties for the link
	in their LSAs.
      </t>
      <t>
	Once the hello protocol has been run on all links, v starts
	the process of generating and sending its own LSA over all its
	links, and of receiving the current LSDB from its neighbors.
	Note that an LSA originated by v must propagate unchanged
	across the network; only v is allowed to change it (and such a
	change must be accompanied by updating the LSA's sequence
	number).  Such an update is triggered by a new link coming up,
	an existing link going down, or a node or link property
	changing.
      </t>
      <t>
	IS-IS and OSPF are in principle similar, although the details
	of the protocol mechanisms and encodings vary.  In both
	protocols, a Type-Length-Value (TLV) is used to encode most
	node and link properties.  In IS-IS, TLVs are used for all
	properties, and a single type of LSA is used; in OSPF, there
	are several types of LSAs, and many (but not all) properties
	are encoded as TLVs.
      </t>
      <t>
	<xref target='RFC1195'/> has examples of "standard" LSAs for
	routing; <xref target='RFC5305'/> has the so-called Traffic
	Engineering LSAs.
      </t>
    </section>
    <section title='Node Properties'>
      <t>
	Here, we give a protocol-independent description of quantum
	node properties; later documents will specify the encoding
	specifically for IS-IS and OSPF.
      </t>
      <t>
	Note that the following list of node properties is a strawman;
	all details are subject to change, and other properties may be
	added as needed.
      </t>
      <t>
	The following node properties are added to the appropriate LSA:
	<figure>
	  <artwork align='center'>
&lt;Qubit-TLV&gt;&lt;NCQ&gt;&lt;NSQ&gt;
&lt;CS-Swap&gt;&lt;Prob&gt;&lt;ExecTime&gt;	    
&lt;Ent-Swap&gt;&lt;Prob&gt;&lt;ExecTime&gt;	    
&lt;Measure&gt;&lt;Prob&gt;&lt;ExecTime&gt;	    
&lt;NDistSch&gt;&lt;DistScheme1&gt;&lt;DistScheme2&gt;
	  </artwork>
	</figure>
      </t>
    </section>
    <section title='Link Properties'>
      <t>
	Only one link property is listed.  It gives the time-fidelity
	tradeoffs of an entanglement operation as a list:
	<figure>
	  <artwork align='center'>
&lt;N-Ent-TO&gt;&lt;time1&gt;&lt;fid1&gt;&lt;time2&gt;&lt;fid2&gt;...
	  </artwork>
	</figure>
	This is interpreted as follows: an entanglement operation may
	be initiated between nodes v and w over link (v, w).  Depending
	on how fast one wants to complete (time-i), the list gives the
	corresponding fidelity of the resulting entanglement (fid-i).
	time-i is given in nanoseconds; fid-i as a number between
	0 and 999999.  THe denominator is 1000000.
      </t>
      <t>
	Note that this link property is symmetric, as entanglement is
	initiated simultaneously at v and w.
      </t>
    </section>
  </section>

  <section title='Security Considerations' anchor='sec-con'>
    <t>
      It is not anticipated that adding these extensions to IS-IS and
      OSPF will present new security hazards to those protocols.
      Since however a common application of entangled pairs is for
      security purposes (such as QKD), it is worth investigating
      whether this application places a higher burden of security on
      the underlying protocols.
    </t>
  </section>

  <section title='Acknowledgments'>
    <t>
      The authors would like to thank the following people for their
      contributions and support to this document: Vesna Manojlovic
      (RIPE NCC) and Axel Dahlberg (QuTech).  Kompella would also like
      to thank Bruno Rijsman for encouraging him to learn about
      Quantum Computing and Networking.
    </t>
    <t>
      Also:
      <figure>
	<artwork align='left'>
       _,'|             _.-''``-...___..--';)
       /_ \'.      __..-' ,      ,--...--'''
      &lt;\    .`--'''       `     /'
       `-';'               ;   ; ;
 __...--''     ___...--_..'  .;.'
(,__....----'''       (,..--''
	</artwork>
      </figure>
    </t>
  </section>
  
  <section anchor="IANA" title="IANA Considerations">
    <t>
      There are no requests as yet to IANA for this document.
    </t>
  </section>
</middle>

<back>
  <references title='Normative References'>
    <?rfc include='reference.RFC.1195'?>
    <?rfc include='reference.RFC.2119'?>
    <?rfc include='reference.RFC.3630'?>
    <?rfc include='reference.RFC.5305'?>
    <?rfc include='reference.RFC.5329'?>
    <?rfc include='reference.RFC.5786'?>
  </references>
  <references title='Informative References'>
    <reference anchor="qubit"
	       target="https://en.wikipedia.org/wiki/Qubit">
      <front>
	<title>Qubit</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="QEnt"
	       target="https://en.wikipedia.org/wiki/Quantum_entanglement">
      <front>
	<title>Quantum Entanglement</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="QNet"
	       target="https://en.wikipedia.org/wiki/Quantum_network">
      <front>
	<title>Quantum Network</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="QTel"
	       target="https://en.wikipedia.org/wiki/Quantum_teleportation">
      <front>
	<title>Quantum Teleportation</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="QFid"
	       target="https://en.wikipedia.org/wiki/Fidelity_of_quantum_states">
      <front>
	<title>Quantum Fidelity</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="QInt">
      <front>
	<title>Quantum internet: A vision for the road ahead</title>
	<author initials='S' surname='Wehner'/>
	<author initials='D' surname='Elkouss'/>
	<author initials='R' surname='Hanson'/>
	<date year='2018'/>
      </front>
      <seriesInfo name='Science' value='362, 6412'/>
    </reference>
    <reference anchor="QDist"
	       target="https://arxiv.org/abs/1803.10111">
      <front>
	<title>Optimizing practical entanglement distillation</title>
	<author initials='F' surname='Rozpedek' fullname='Filip Rozpedek'/>
	<author initials='T' surname='Schiet' fullname='Thomas Schiet'/>
	<author initials='L' surname='Thinh' fullname='Le Phuc Thinh'/>
	<author initials='D' surname='Elkouss' fullname='David Elkouss'/>
	<author initials='A' surname='Doherty' fullname='Andrew C. Doherty'/>
	<author initials='S' surname='Wehner' fullname='Stephanie Wehner'/>
	<date year="2018"/>
      </front>
      <seriesInfo name='Phys. Rev. A' value='97, 062333'/>
    </reference>
    <reference anchor="QKD"
	       target="https://en.wikipedia.org/wiki/Quantum_key_distribution">
      <front>
	<title>Quantum Key Distribution</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="NVC"
	       target="https://en.wikipedia.org/wiki/Nitrogen-vacancy_center">
      <front>
	<title>Nitrogen-vacancy center</title>
	<author/>
	<date/>
      </front>
    </reference>
    <reference anchor="NVD">
      <front>
	<title>
	  Deterministic delivery of remote entanglement on a quantum network
	</title>
	<author initials='P.C' surname="Humphreys" fullname='P. C. Humphreys et al.'/>
	<date year='2018'/>
      </front>
      <seriesInfo name="Nature" value="558"/>
    </reference>
    <reference anchor="NVDD">
      <front>
	<title>
	  Loophole-free Bell inequality violation using electron spins
	  separated by 1.3 kilometres
	</title>
	<author initials='B' surname="Hensen"/>
	<author surname='others'/>
	<date year='2015'/>
      </front>
      <seriesInfo name="Nature" value="526"/>
    </reference>
    <reference anchor="IonTrap">
      <front>
	<title>
	  Modular entanglement of atomic qubits using photons and phonons
	</title>
	<author initials='D' surname="Hucul"/>
	<author surname='others'/>
	<date year='2015'/>
      </front>
      <seriesInfo name="Nature Physics" value="11(1)"/>
    </reference>
    <reference anchor="NAtom">
      <front>
	<title>
	  Efficient Teleportation Between Remote Single-Atom Quantum Memories
	</title>
	<author initials='C' surname="Noelleke"/>
	<author surname='others'/>
	<date year='2013'/>
      </front>
      <seriesInfo name="Physical Review Letters" value="110, 140403"/>
    </reference>
    <reference anchor="QAEM">
      <front>
	<title>
	  Quantum repeaters based on atomic ensembles and linear optics
	</title>
	<author initials='N' surname="Sangouard"/>
	<author surname='others'/>
	<date year='2011'/>
      </front>
      <seriesInfo name="Reviews of Modern Physics" value="83, 33"/>
    </reference>
  </references>
</back>
</rfc>