The invention is generally related to the tech nology of sample handling in both room temperature and cryogenic environments. In particular the invention is related to protecting the samples from harmful effects of environmental conditions when the sample is not un dergoing active measurements in the cryogenic environ ment.

BACKGROUND OF THE INVENTION Many applications necessitate cooling a rela tively small piece of material, often referred to as a sample, down to very low temperatures for the duration of various measurements and operation. Examples of such samples include, but are not limited to, quantum circuit elements used in quantum computing. Other examples are for example pieces of sophisticated materials like gra phene, other atomic-level thin-film materials, carbon nanotubes and fullerenes, and the like. Low temperatures mean here temperatures that can only be achieved in cryogenic cooling systems: temperatures lower than 10 K, typically lower than 4 K, and in many cases in the order of only some millikelvins. The need to minimize conductive and convective transfer of heat necessitates creating vacuum conditions in addition to the very low temperature.

A feature characteristic in particular to quan tum circuit elements, but often needed in also other kinds of sample measuring applications, is the require ment of providing a number of very high frequency signal connections to and from the sample. The frequencies in volved may be in the order of several GHz. The signal connections should not create any significant heat load that could make it more difficult to maintain the de sired very low temperature.

It has been noticed that samples of the kind described above may undergo undesired deterioration of their characteristics if subjected to environmental con ditions such as ordinary air, airborne moisture, and other impurities. A natural way to avoid such deterio ration would be to manufacture the samples close to the cryostat in which the measurements are to be performed, and to insert the samples into the cryostat as quickly as possible after manufacturing. However, such close- quarter logistics are not always possible, and samples may need to be transported over even very long dis tances. Some samples also need to be held in storage for later measurements or for transportation for consider able periods of time.

SUMMARY

It is an objective to provide an arrangement for enabling the handling and measuring of samples of the kind described above with reduced risk of their characteristics deteriorating. Another objective is that the arrangement allows repeated access to the sam ple without sacrificing the protection provided. A fur ther objective is to enable re-using and recycling any valuable structures and materials involved in handling and measuring the samples. A yet further objective is to provide considerable freedom in the number and struc ture of signal connections that can be made to the sam ple.

The objectives of the invention are achieved by utilizing a vacuum-tight, openable and closable sam ple cell for the sample, with integrated vacuum-tight signal connections and good thermal connection to a sam ple enclosed in the sample cell. According to a first aspect there is provided a sample cell for holding a sample to be placed in a cryogenically cooled environment. The sample cell com prises an airtight, openable and closable enclosure; within said enclosure a sample base for receiving the sample; a refrigerator attachment for attaching the sam ple cell to a refrigerated body of the cryogenically cooled environment; a thermal connection between the sample base and the refrigerator attachment; and one or more airtight connectors for establishing electric con nections between inside and outside of the enclosure.

According to an embodiment the sample cell com prises an evacuation channel between inside and outside of the enclosure for evacuating the enclosure after closing. This involves the advantage that attaching the sample, making connections, and closing the enclosure can be made conveniently without having to pay immediate attention to very particular environmental conditions, and the sample can be subsequently isolated from harmful effects of atmospheric conditions by evacuating the en closure.

According to an embodiment the evacuation chan nel comprises a conduit through a structure of said enclosure, and the sample cell comprises a closing valve for selectively allowing and preventing flow of gaseous media through the conduit. This involves the advantage that sealing the enclosure against surrounding atmos pheric conditions can be accomplished conveniently with very little external hardware.

According to an embodiment the closing valve comprises a closing member movable between an open po sition and a closed position, of which in said open position said closing member allows gaseous media to flow through said conduit and in said closed position said closing member prevents gaseous media from flowing through said conduit. This involves the advantage that a relatively simple, yet robust and reliably functioning way of closing the conduit is readily available.

According to an embodiment the sample cell com prises a piece of deformable sealing material at such a part of the conduit that said closing member is arranged to occupy in the closed position. This involves the advantage that the closure of the conduit can be made sufficiently airtight with relatively simple mechanical means.

According to an embodiment the closing valve comprises a cavity at an angle against said conduit, said cavity having threads, and the closing member com prises a threaded pin arranged for longitudinal movement in said threaded cavity in response to turning on said threads. This involves the advantage that a relatively simple, yet robust and reliably functioning way of clos ing the conduit is readily available.

According to an embodiment the refrigerator attachment defines an essentially planar outer surface of said sample cell; the sample base defines an essen tially planar inner surface of the sample cell, said inner surface being parallel with said outer surface, and the thermal connection comprises a layer of a ther mally conductive material between said inner and outer surfaces. This involves the advantage that mechanically simple and easily manufactured parts can be used to implement the refrigerator attachment, the sample base, and the thermal connection.

According to an embodiment said thermally con ductive material is a material that remains thermally conductive in sub-kelvin temperatures. This involves the advantage that the sample can be cooled to even sub- kelvin temperatures while still inside and protected by the sample cell.

According to an embodiment said thermally con ductive material comprises one of the following: alumi num, copper, gold. This involves the advantage that the availability, tooling characteristics, and inherent ma terial characteristics of the material are well known, and known to be suitable for the purpose in question.

According to an embodiment said enclosure com prises a body part in which said sample base is located and a lid part removably attached to said body part to close an opening in said body part. This involves the advantage that the basic structure of the sample cell can be kept relatively simple without compromising the highly advantageous functional characteristics it has.

According to an embodiment the sample cell com prises an electrically conductive seal between the body part and the lid part. This involves the advantage that the body part and the lid part can be used to establish a continuous, electromagnetically shielding structure around the sample in the sample cell.

According to an embodiment the electrically conductive seal is made of a superconductive material. This involves the advantage that the seal enables cre ating a seamless superconductive path between parts of an openable sample cell in case superconductive materi als are used also for the other parts.

According to an embodiment the sample cell is made of a superconductive material. This involves the advantage of providing a particularly good electromag netic shielding, including low-frequency magnetic shielding, for the sample at the eventual operating tem peratures.

According to an embodiment the sample cell com prises a handling attachment for removably attaching the sample cell to a probe for inserting the sample cell into a cryogenic cooling apparatus. This involves the advantage that the sample cell can be used in sample changes in which the whole cryogenic cooling system does not need to be intermittently thermalized and opened.

According to a second aspect there is provided an arrangement for cooling a sample in a cryogenically cooled environment. The arrangement comprises a sample cell of the kind described above, a cryogenic cooling apparatus that comprises a refrigerated body, and a sam ple cell receiving surface of said refrigerated body for receiving said sample cell into thermally conductive contact with said refrigerated body.

According to an embodiment said refrigerated body comprises, or defines a thermally conductive con nection to, a mixing chamber of a dilution refrigerator. This involves the advantage that the arrangement can be used to cool down the sample to temperatures achievable with the dilution refrigerator, which may be in the order of only a few millikelvins.

According to a third aspect there is provided a method for handling a sample to be placed in a cryo- genically cooled environment. The method comprises plac ing said sample into thermally conductive contact with a sample base in a sample cell that defines an openable and closable airtight enclosure, closing said enclosure, and evacuating said enclosure before placing the sample cell in said cryogenically cooled environment.

According to an embodiment the method comprises protecting the sample with a priming chemical treatment. This involves the advantage that additional protection against environmental effects can be achieved for exam ple if there are delays between sample fabrication and the evacuation of the enclosure.

According to an embodiment the protecting in volves using hexamethyldisilazane for said priming chem ical treatment. This involves the advantage that good protective priming can be achieved with known charac teristics.

According to an embodiment the method comprises storing the sample in said closed and evacuated enclo sure for a storage period before placing the sample cell in said cryogenically cooled environment. This involves the advantage of having the sample safe from the effects of environmental conditions despite the length of the waiting period before it can be actually placed in the cryogenically cooled environment.

According to an embodiment the method comprises establishing electric connections to and from said sam ple through airtight connectors between inside and out side of said enclosure. This involves the advantage that electric measurements and operations can be accomplished in the sample without having to open the enclosure and maintaining the sample within the protection offered by the sample cell.

According to an embodiment the method com prises, before re-opening said enclosure, establishing pressure balance between inside and outside of said en closure, and after said pressure balance has been es tablished, opening said enclosure. This involves the advantage that the pressure difference between inside and outside of the enclosure does not make its handling more difficult at the step of opening the enclosure.

According to an embodiment the step of evacu ating the enclosure comprises closing an evacuation channel that comprises a conduit through a structure of said enclosure, and the method comprises re-opening said evacuation channel after said pressure balance has been established or as a part of establishing said pressure balance. This involves the advantage that a mechanically simple and functionally reliable way can be offered for implementing all operations that involve changing the pressure balance between inside and outside of said en closure.

According to an embodiment the re-opening of said evacuation channel comprises cleaning said conduit of sealing material that was used at a preceding method step to seal the evacuation channel when closed. This involves the advantage that the sample cell can be made ready for another round of use with only little work. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate em bodiments of the invention and together with the de scription help to explain the principles of the inven tion. In the drawings:

Figure 1 illustrates a principle of a sample cell,

Figure 2 illustrates an example embodiment of a sample cell,

Figure 3 illustrates an example embodiment of a sample cell in open configuration without an inserted sample,

Figure 4 illustrates the example embodiment of sample cell of fig. 3 in closed configuration with an inserted sample,

Figure 5 illustrates an example of a sample cell in a cryogenically cooled environment,

Figure 6 illustrates an example of inserting a sample cell into a cryogenically cooled environment, Figure 7 illustrates a method,

Figure 8 illustrates a method, and Figure 9 illustrates a possible additional step in a method.

DETAILED DESCRIPTION Fig. 1 illustrates schematically some examples of parts and features of a sample cell for holding a sample to be placed in a cryogenically cooled environ ment. The sample cell comprises an airtight, openable and closable enclosure 101 that is structurally strong and integral enough so that it can stand a pressure difference between atmospheric pressure on its outside and vacuum on its inside. The purpose of the vacuum inside the enclosure 101 is to minimize effects of at mospheric constituents on a sample that can be held enclosed in the enclosure 101 for long periods of time. The quality of the internal vacuum that the enclosure

101 is to withstand should be at least in the order of 10 ³ Pa, and possibly smaller such as down to 10 ^_1 Pa for example. The periods of time for which a sample may be held in the enclosure 101 may be in the order of days, weeks, months, or even years, and the quality of the vacuum should not essentially deteriorate during such periods.

Within the enclosure 101 a sample base 102 is provided for receiving a sample. Examples of samples that the sample base 102 might receive include but are not limited to quantum computing chips such as quantum processor chips, quantum resonator chips and the like, typically attached to a piece of circuit board or a corresponding substrate. The sample base 102 may be structurally as simple as an essentially flat surface onto which the sample can be attached with attachment means such as screws, solder, ultrasonic welding, or thermally conductive glue.

The sample cell comprises a refrigerator at- tachment 103 for attaching the sample cell to a refrig erated body of a cryogenically cooled environment. A thermal connection 104 exists between the sample base

102 and the refrigerator attachment 103 for conducting heat from a sample attached to the sample base 102 to the refrigerator attachment 103 and further to the re frigerated body of a cryogenically cooled environment. The meaning is to allow utilizing the cooling capability of the cryogenically cooled environment to bring the sample to as low temperature as possible, which is eas- rest if there is a chain of thermally well conducting materials and interfaces all the way from the sample itself to the mechanism that cools the cryogenically cooled environment.

How the refrigerator attachment 103 is advan tageous to implement in practice depends very much on how the refrigerated body of the cryogenically cooled environment looks like. As an example, it may be known that the refrigerated body of the cryogenically cooled environment offers a planar surface of certain size, to which samples and/or sample holders are to be attached. In such a case the refrigerator attachment 103 may be a similar planar surface, possibly augmented with screw holes, spring-loaded connectors, and/or other ways of making and keeping a tight contact between the two pla nar surfaces. As another example the refrigerated body of the cryogenically cooled environment may comprise one or more slots, one or more pegs, and/or one or more internal or external screw threads for attaching samples or sample holders. In such a case it is advantageous to make the refrigerator attachment 103 comprise a corre sponding set of pegs, slots, and/or external or internal screw threads for attaching the sample cell to the re frigerated body of the cryogenically cooled environment.

One or more airtight connectors 105 are pro vided for establishing electric connections between in side and outside of the enclosure 101. The airtight connectors 105 are provided for the purpose of conduct ing electric signals of desired kind and number to and/or from a sample that is held inside the enclosure 101. The airtight connectors 105, just as any other structural parts of the enclosure 101, should be suffi ciently airtight to allow maintaining the desired qual ity of vacuum inside the enclosure 101 for those periods for which samples are to be held in the enclosure 101. At the same time the airtight connectors 105 should be designed so that they allow conducting electric signals of the kind used in quantum computing applications. This may mean oscillating signals on frequencies in the order of several GHz, which may require the airtight connect ors 105 to be coaxial, RF-rated connectors such as TNC or SMA connectors. Airtight connectors of this kind, manufactured and marketed for making hermetically sealed electric connections across bulkheads, are readily available from manufacturers such as Huber+Suhner, Pfaffikon, Switzerland, for example.

Internal connections 106 may be provided inside the enclosure 101 for allowing the conducting of elec tric signals between one or more of the airtight con nectors 105 and a sample attached to the sample base 102. Such internal connections 106 should be constructed for adequate performance on the frequencies and signal energies that are to be expected, for example using RF- rated transmission lines.

The sample cell may comprise an evacuation channel 107 between inside and outside of the enclosure 101 for evacuating the enclosure 101 after closing. An evacuation channel 107 is not necessary if the desired quality of vacuum inside the enclosure 101 can be achieved through other means, for example by performing the closing of the enclosure 101 (after a sample has been attached to the sample base 102 and the necessary electric connections inside the enclosure 101 have been completed) under vacuum conditions, for example in a glove box or a vacuum chamber with suitable built-in actuators. However, providing an evacuation channel 107 may create advantages in the form of simplifying the evacuation process. Examples of this are described in more detail later in this text.

If an evacuation channel 107 is provided, it may comprise a conduit through a structure of the en closure 101, for example through one of its walls. The sample cell may comprise a closing valve 108 for selec tively allowing and preventing flow of gaseous media through such a conduit. Such a structure allows keeping the closing valve 108 open for the time it takes to evacuate the sample cell, and then closing the closing valve 108 so that further flow of gaseous media through the conduit is prevented.

Fig. 2 illustrates an example embodiment of a sample cell. The entity that has been described above as the enclosure 101 comprises a body part 201 and a lid part 202. The sample base (not shown in fig. 2) is located in the body part 201. The lid part 202 is re movably attached to the body part 201 to close an opening in the body part 201. In the embodiment shown in fig. 2 the body part 201 comprises a base plate and a cylin drical housing, so that the base plate closes one end of the cylindrical housing and said opening is at the other end of the cylindrical housing. The lid part 202 is a round flange, the diameter of which matches the outer diameter of the cylindrical housing in the body part 201. A seal 203 can be placed between the lid part 202 and the body part 201. The seal 203 may be for example an indium seal, for the purpose of hermetic sealing and facilitating superconductive connection be tween the body part 201 and the lid part 202 when cooled to sufficiently low temperatures. Other possible mate rials of the seal include but are not limited to lead and various lead-indium alloys.

Matching screw holes are provided in both the lid part 202 and the body part 201; see screw holes 204 and 205 as an example. Two screws 206 and 207 are shown in fig. 2 as examples. By placing screws similarly into all screw holes and tightening them evenly the lid part 202 can be pressed tightly against the edges of the opening in the body part 201, squeezing the seal 203 therebetween, so that an airtightly closed enclosure is formed. This form of attaching underlines how a good sealing material should be relatively soft and deform able, and - if required - capable of becoming supercon ductive at those temperatures that are involved in using the sample cell and sample for measurements and/or op eration.

It is advantageous to manufacture the basic structure of the sample cell (which in the embodiment of fig. 2 means the body part 201 and the lid part 202) of a superconductive material. Calling a material su perconductive means that the material is known to be capable of exhibiting superconductivity at temperatures at which the sample, for the holding of which the sample cells is used, is to be operated. Taken that in the applications meant here the sample is or at least com prises typically a quantum computing circuit, the tem peratures at which the sample is to be operated are close to absolute zero, typically less than 1 K and in many cases as low as 10 mK or even lower. Superconductive materials suitable for manufacturing the basic structure of the sample cell include but are not limited to alu minum, niobium, tantalum, titanium, and superconductive alloys of these.

Manufacturing the basic structure of the sample cell of a superconductive material involves the ad vantage that the sample cell becomes an effective shield against external electromagnetic interference that could otherwise affect the sample during operation. This also means that the electromagnetic shielding of the sample becomes largely independent of what kind of shielding the structures of the cryogenically cooled environment could inherently offer. Maintaining good shielding all around the sample may require that also the seal 203 is made of electrically conductive or su perconductive material. An example of an advantageous material for the seal 203 is indium, but it is also possible to utilize other materials that have effective sealing and conductive (or superconductive) properties.

Fig. 3 illustrates a cross section of a sample cell of the kind shown in fig. 2 above. In this embod iment the evacuation channel is provided, and comprises a conduit 301 through a structure (here: through a part of the base plate of the body part 201) of the enclosure. The closing valve comprises a closing member 302 that is movable between an open position and a closed posi tion. In the open position the closing member 302 allows gaseous media to flow through the conduit 301, and in the closed position the closing member 302 prevents gas eous media from flowing through the conduit 301.

In the embodiment shown in fig. 3 the closing member 302 has the form of a threaded pin that fits in a cavity 303 located at an angle against the conduit 301. In this embodiment the threaded cavity is at a right angle above the conduit 301 in the base plate and has internal threads. The matching threads of the clos ing member 302 and the cavity 303 mean that the former is arranged for longitudinal (here: vertical) movement in the threaded cavity 303 in response to turning on said threads. This longitudinal movement translates into similar longitudinal movement of the smaller diameter peg 304 at the lower end of the closing member 302 in the smaller diameter hole 305 that extends from the bottom of the cavity 303 further downwards, intersecting the conduit 301. The open position of the closing member 302 is one in which the smaller diameter peg 304 does not block the conduit 301, and the closed position of the closing member 302 is one in which the smaller di ameter peg 304 is so low down in the smaller diameter hole 305 that it blocks the conduit 301. Fig. 3 shows the closing member 302 completely out of the cavity 303 for graphical clarity, but it should be noted that in the open position it can be on its threads in the cavity 303, although high enough for the smaller diameter peg 304 not blocking the conduit 301.

In order to ensure complete and airtight block ing of the conduit when the closing member 302 is in its closed position, the sample cell may comprise a piece 306 of deformable sealing material at such part of the conduit 301 that the closing member 302 is arranged to occupy in its closed position. In the embodiment shown in fig. 3 a small, preferably somewhat spherical piece of indium or other deformable sealing material has been placed on the bottom of the smaller diameter hole 305, where a recess may be provided for temporarily holding the piece 306 of deformable sealing material in place. The longitudinal movement of the smaller diameter peg 304 in the smaller diameter hole 305, when the closing member 302 is turned on its threads, causes the piece 306 of deformable material to deform and fill all pos sible empty spaces around the smaller diameter peg 304 that could otherwise allow air to leak back into the evacuated enclosure.

In the embodiment of fig. 3 a connector 307 is provided at the outer end of the conduit 301. The purpose of such a connector 307, if provided, is to make it easier to connect an inlet of a vacuum suction pump to the sample cell, for evacuating the sample cell after installing the sample and closing the lid.

In the embodiment of fig. 3 the refrigerator attachment of the sample cell defines an essentially planar outer surface 308 of the sample cell. In the orientation shown in fig. 3 this is the bottom surface of the sample cell. The sample base 102 is located on the bottom of the cylindrical void that is defined by the cylindrical housing and that extends partly into the base plate of the body part 201. The sample base 102 defines an essentially planar inner surface of the sam ple cell, said inner surface being parallel with said outer surface 308. The thermal connection that was de scribed with reference designator 104 in fig. 1 com prises a layer 309 of a thermally conductive material between said inner and outer surfaces. Just like with superconductivity above, calling a material thermally conductive means that the material remains thermally conductive in sub-kelvin temperatures. Aluminum is a good example, so if the basic structure of the sample cell is made of aluminum, the layer 309 of thermally conductive material may be simply that wall of the sam ple cell that is between the sample base 102 and the refrigerator attachment 103. Other materials that are known to be good thermal conductors in sub-kelvin tem peratures include but are not limited to copper and gold.

Another example of a feature of the refriger ator attachment is the hole 310 in the base plate of the body part 201. A screw or other attachment means can be placed in the hole 310 for enabling a tight and thermally well conducting contact to a refrigerated body of the respective cryogenically cooled environment.

Fig. 4 is a cross section of a sample cell according to the embodiment of fig. 3 in closed config uration. A sample 401, such as a quantum computing chip or quantum resonator chip for example, has been attached to the sample base 102, and the necessary electric con nections have been established between contact points of the sample 401 and the respective airtight connectors 105. In this embodiment a bonding wire 402 connects a contact point (not separately shown) of the sample 401 to the appropriate conductor of a transmission line 403, the other end of which is in contact with the inner end of the airtight connector 105. The lid part 202 has been pressed against the upper edge of the cylindrical hous ing in the body part 201 by tightening the screws 206 and 207, so that the seal 203 that was visible in the exploded view of fig. 3 is not visible any more. The closing member 302 has been turned all the way in on its threads, so that it prevents gaseous media from flowing through the conduit 301: the smaller diameter peg 304 fills completely the smaller diameter hole and thus blocks the conduit 301. If a piece of deformable sealing material such as that shown as 306 in fig. 3 was there, the downward movement of the smaller diameter peg 304 has squeezed it into thin layers that fill and seal all gaps that otherwise could allow air to leak through.

Fig. 5 illustrates an example of an arrangement for cooling a sample in a cryogenically cooled environ ment. The sample is not itself visible in fig. 5, because it is inside the sample cell 501. The cryogenic cooling apparatus 502 is a cryostat that comprises a refriger ated body 503, which in this case is the mixing chamber of a dilution refrigerator. The arrangement comprises a sample cell receiving surface of the refrigerated body 503 for receiving the sample cell 501 into thermally conductive contact with the refrigerated body 503. A set of radiation shields 504, 505, and 506 surrounds the innermost part of the cryostat, of which the outermost radiation shield 506 also constitutes a part of the vacuum can that encloses the inner parts of the cryo stat. Special kind of cabling 507, 508, and 509 is used between the various stages of the arrangement so that signals can be conveyed in both directions between the sample and the surrounding room temperature environment. In this embodiment the ends of the innermost cables 507 may be connected to the airtight connectors that form part of the sample cell 501.

Fig. 6 illustrates another example of an ar rangement for cooling a sample in a cryogenically cooled environment. The sample is inside the sample cell 601. The cryogenic cooling apparatus 602 is a cryostat that comprises a refrigerated body 603, which in this case is a cold plate that comprises a thermally conductive connection to a mixing chamber of a dilution refriger ator 604. A surface of the cold plate serves as the sample cell receiving surface of the refrigerated body 603 for receiving said sample cell 601 into thermally conductive contact with the refrigerated body 603.

The arrangement of fig. 6 differs from that of fig. 5 in that the cryostat is equipped with a so-called sample changer, which comprises an airlock 605 and a set of openable and closable baffles 606 and 607 in the radiation shields 608, 609, and 610. An elongated probe 611 can be used to bring the sample cell 601 in through the airlock 605 and through concentric openings in the radiation shields 608, 609, and 610. The airtight con nectors in the sample cell 601 engage with matching connectors in the refrigerated body 603 upon the sample cell 601 making contact with and becoming attached to the refrigerated body 603, so in this embodiment the cabling 612, 613, and 614 run only between the fixed stages of the cryostat. The attachment between the sam ple cell 601 and the upper end of the probe 611 can be disconnected, at least to the extent of not conducting heat, once the sample cell 601 is in place so that the thermal conductivity of the probe does not load the cooling capacity of the cryostat.

Fig. 7 illustrates an example of a method for handling a sample to be placed in a cryogenically cooled environment. Step 701 of the method comprises placing the sample into thermally conductive contact with a sam ple base in a sample cell that defines an openable and closable airtight enclosure. The sample cell is prefer ably of the kind described in at least one of the em bodiments above. In a typical case, electric connections need to be made to and from the sample, so the method of fig. 7 comprises making such connections in step 702, for example by wire bonding as was described earlier with reference to fig. 4.

Step 703 comprises closing the enclosure, for example by screwing a lid part over an opening of a housing in a body part. Step 704 comprises evacuating the enclosure before placing the sample cell in the cryogenically cooled environment. If the sample cell is of the kind shown in figs. 3 and 4, this can be accom plished by connecting the inlet of a vacuum suction pump to the connector at the outer end of the conduit in the base part and allowing the pump to run until the vacuum at its inlet is of sufficient quality. Step 705 com prises preventing further flow of gaseous media through the conduct by closing an associated valve, for example by turning the threaded closing member of figs. 3 and 4 all the way in on its threads.

If the sample does not need to be operated immediately, the method may comprise storing the sample in the closed and evacuated enclosure for a storage period before placing the sample cell in the cryogeni- cally cooled environment, as shown as step 706 in fig. 7. Eventually the sample cell with the sample inside is placed in the cryogenically cooled environment as shown as step 707 in fig. 7. Step 7 comprises also establishing electric connections to and from the sample through air tight connectors between inside and outside of the en closure. Additionally step 707 may be interpreted to comprise all those steps that belong to the normal way of performing measurements in the cryogenically cooled environment, including but not being limited to evacu ating and cooling down the cryostat, subjecting the sam ple to input signals and collecting output signals from the sample.

When no more operating of the sample in the cryogenically cooled environment is intended, the sample cell is removed from the cryogenically cooled environ ment as shown as step 708 in fig. 7. This step may naturally involve substeps that may be necessary for ventilating and thermalizing the cryostat, or for using a probe to detach and remove a sample cell through a sample changer. The possible return path from step 708 to step 706 means that at least in some cases the sample could be stored for further measurements, for transpor tation, and/or for some other purpose without opening the sample cell at this time. Step 709 comprises, before re-opening the enclosure, establishing pressure balance between inside and outside of the enclosure. This can be done for example by opening a valve that closes a conduit through which the enclosure was evacuated, and/or loosening a screw or other attachment means that holds a lid part or other kind of an openable part in place. After said pressure balance has been established, the method comprises opening the enclosure at step 710. The sample can now be disconnected from any electric connections internal to the enclosure, and removed from the enclosure.

The sample cell is intended to be reusable. Therefore, while steps 704 and 705 involved evacuating the enclosure through an evacuation channel and subse quently closing the evacuation channel (which comprises a conduit through a structure of the enclosure), the method comprises re-opening said evacuation channel af ter pressure balance has been established (or as a part of establishing said pressure balance) between inside and outside of the enclosure. In fig. 7 there is a step 711, which comprises removing remnants of used seals, such as the seal 203 and the piece 306 of deformable sealing material. The remnants of the seal 203 may be removed by scrubbing the appropriate surfaces of the body part and the lid part. The remnants of the piece 306 of deformable sealing material may be removed by running a suitable cleaning instrument through the con duit 301. The last-mentioned may be constitute a part of the step where pressure balance is established be tween inside and outside of the enclosure before re opening the enclosure: running the cleaning instrument through the conduit may clear the way for surrounding air to flow in and fill the enclosure.

Fig. 8 illustrates another embodiment of a method for handling a sample to be placed in a cryogen- ically cooled environment. In fig. 8 it is assumed that either the sample cell does not comprise an evacuation channel, or for some purpose it is not used but it is kept closed all the time. Those steps in the method of fig. 8 that are the same as corresponding steps in fig. 7 are numbered with the same reference designators and need not be described in more detail here. After the electric connections internal to the sample cell have been completed in step 702, the sample cell is closed under controlled conditions, like a controlled atmos phere or vacuum conditions for example, at step 801. This can be accomplished for example by placing the parts of the still open sample cell in a controlled environment such as a glove box, in which environmental parameters are carefully controlled: as an example, ox ygen and humidity levels may be substantially reduced compared to atmospheric conditions, and/or the con trolled environment may involve vacuum conditions. One may then utilize any available manipulating means to close and seal the enclosure in the special conditions that prevail in the controlled environment. If a vacuum chamber with suitable mechanical manipulators is avail able, it can be used as a controlled environment in step 801. Otherwise the method in fig. 8 is similar to that of fig. 7, with the possible exception that if at least one of steps 709, 710, or 711 in fig. 7 involved removing remnants of sealing material from the evacuation chan nel, a corresponding part of the similarly numbered step may not be needed in fig. 8 if there was no evacuation channel or if it was not to be used either during the next reuse of the sample cell.

Fig. 9 illustrates how any of the methods of figs. 7 or 8 may comprise protecting the sample with a priming chemical treatment at step 901. This may be done quite early in the process, for example already before placing the sample into thermally conductive contact with the sample base in the sample cell. The priming chemical treatment may protect the sample against harm ful environmental effects, for example if there occurs a delay before the sample cell can be closed and evac uated. An example of a chemical suitable for a priming chemical treatment is hexamethyldisilazane (HMDS), which has the property of evaporating when evacuated, so it is practical for providing protection under the period during which the sample would otherwise be sub jected to the atmospheric conditions of a normal indoor environment.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims.